Hi jamccor,
Your original question has been going round in my head. I've wanted to post the answer I know to be true, but it seemed complicated. So, what I want to write here will be as simple as I can make it, but it's not short. If can catch my drift, I believe you have the key to spiritual safety.
I believe Paul's exposition of the effectiveness of Christ's death.
Romans 6 (NKJV)
5 For if we have been united together in the likeness of His death, certainly we also shall be [i]in the likeness[/i] of [i]His[/i] resurrection, 6 knowing this, that our old man was crucified with [i]Him,[/i] that the body of sin might be done away with, that we should no longer be slaves of sin.
KJV: 5 For if we have been planted together in the likeness of his death, we shall be also [i]in the likeness[/i] of [i]his[/i] resurrection: 6 Knowing this, that our old man is crucified with [i]him[/i], that the body of sin might be destroyed, that henceforth we should not serve sin.
Modern version refer to 'self' rather than 'old man'. (Note, it was 'our' 'old man' who Christ took into His death on behalf of humanity.)
The other thing to note in the KJV is the present tense. 'Our old man [u]is[/u] crucified'. This is a statement which is eternally true, not merely historically true in our time frame as the 'was' of the NKJV appears to imply. This eternal aspect of Christ's death is to the fore again in John's words here:
Revelation 5:6 (KJV)
And I beheld, and, lo, in the midst of the throne and of the four beasts, and in the midst of the elders, stood [u]a Lamb as it had been slain[/u], having seven horns and seven eyes, which are the seven Spirits of God sent forth into all the earth.
John it was who noted John the Baptist's proclamation: 'Behold the Lamb of God who [u]takes[/u] away the sin of the world.' (John 1:29)
We have always to remember that as we are in Christ, we are in eternity; that is, [i][b]now[/i][/b] we are in eternity, [u]in[/u] that eternal truth of the Lamb just slain, which is the foundation of John's statement in his first epistle, chapter 1:7
But if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin. (Note again there is a plural pronoun 'we' just as the old man was 'our's.)
The reason I'm laying all this out, is it is foundational scripture for understanding [i]how[/i] we are kept from the wicked one. What I posted earlier about our co-operation with God is also essential, although the [i]power[/i] is all God's available to us on [i]His[/i] terms.
So.... you asked...
to keep the bad spirits from having a foothold in my life?
to which I wanted to reply with an opposite thought, which is that there are
[i]two[/i] ways we may have footholds in our lives.
One is, that after we have given our lives to the Christ, the more we press on in the Spirit, the more likely we are to find issues we have never had to deal with but which have always been there as part of us. These may be assumptions we have always made about the way life works, or things we have always done; ways we have always dealt with regularly occurring situations, ways of thinking which have never been challenged by the Spirit of God previously. The enemy immediately wants us to suspect we never knew God in the first place, but this is unlikely to be the case (although it may be), so (I think) it's important to resist the temptation to rake over our whole Christian past. Rather, the place to go is Christ's death and there to reaffirm our commitment to be identified with Him in it on our own behalf. This is where the release comes and new thoughts (etc) can begin to strike our understanding as the Spirit is free to reveal His truth to us. Paul refers to spiritual events like these, as the pulling down of strongholds. Sometimes there is more of a battle than I've described, but the principle is the same, and thus sin [u]does not[/u] have dominion over us.
Young phrases those two verses from Romans 6 like this: 5 For, if we have become planted together to the likeness of his death, [i]so[/i] also we shall be of the rising again; 6 this knowing, that our old man was crucified with [i]him[/i], [u]that the body of the sin may be made useless, for our no longer serving the sin[/u];
The reason I'm labouring this, is that while sin is spiritual, it is outworked by the lusts of the mind of the flesh, [i]by our bodies[/i] and it is here that if there are other spirits involved, we will feel their effects by thoughts and physical inclinations which are counter to what the Holy Spirit is bringing to our spirit, soul and flesh.
In principle then, as we literally stop agreeing with things counter to the Holy Spirit, those inclinations will shrivel up and die.
The New Testament refers to this as 'mortify' or 'put to death'
Romans 8:13
[u]For if[/u] ye live after the flesh, ye shall die: but [u]if ye[/u] through the Spirit do mortify the deeds of the body, [u]ye shall live[/u].
and again, as with [i]keeping ourselves[/i], it is [u]we[/u] who do the 'mortify'ing with the Holy Spirit's [i]help[/i]. This is an accurate description of the spiritual dynamic that releases us from our flesh, thus making it impossible for any other 'spirit' to gain a (new) foothold. But, we may find, in the process of addressing such footholds as seem to have been there all our lives, that there is already a spirit involved, whose mindset we seem to have appropriated but never noticed before. :-o I think this is why Paul returns us to the renewing of the spirit of our mind, several times in his letters. (Rom 12:2, Eph 4:23.) This begins with regeneration (Titus 3:5) and impacts everything thereafter ( 2 Cor 4:16).
The other way footholds arise, is by our opening ourselves to spiritual interference through actions we can find (within our limited understanding) no definte reason not to pursue. However, we later discover we were ignorant of a spiritual danger, and immediately stop doing that thing. In these situations, God is gracious to deliver us swiftly (in my experience), knowing we had no idea what we were getting into.
But, therefore, it is spiritually most unwise [u]knowingly[/u] to [i]do[/i] anything which opens up an entrance through sin, for other spirits, by choosing to ignore the clear guidance of scripture. Sins of the flesh are named in Gal 5:19, 20 and Romans 1:28 - 32 and other places in the New Testament, and are all associated with idolatry - opposite to worshiping God - and also are clearly laid out in the Old Testament in various places, some of them most explicitly if you read around the lead up to and fall-out from the golden calf in Exodus. These activities, all to be avoided, [u]are[/u] the playground of devils (1 Cor 10:20, 21).
In other words, your [i]protection[/i] from 'bad spirits' is as real as your claim to holiness and righteousness through Christ, who also is made to us wisdom and redemption (1 Cor 1:29 - 31), v 29 'That no flesh should glory in his presence.'
Isa 40:1 - 5
Heb 12:11 - 13