Personally, I believe God can wipe out Satan is a quick second if he really wanted to, but he has plans for Satan. See scripture below in Revelation 20. Satan is a created being. God created man and he almost wiped out mankind in Noah's day.
Revelation: 20:1-2, 10
And I saw an angel come down from heaven, having the key of the bottomless pit and a great chain in his hand. And he laid hold on the dragon, that old serpent, which is the Devil, and Satan, and bound him a thousand years,..
10And the devil that deceived them was cast into the lake of fire and brimstone, where the beast and the false prophet are, and shall be tormented day and night for ever and ever.
As for your question concerning how to defend yourself against Satan, read and study Ephesians 6:10-18
Finally, my brethren, be strong in the Lord and in the power of his might. Put on the whole armour of God, that you may be able to stand against the wiles (schemes, tricks, traps) of the devil.
Wherefore take unto you the whole armour of God, that you may be able to withstand in the evil day, and having done all, to stand. Stand therefore, having your loins girt about with truth, and having on the breastplate of righteousness;
And your feet shod with the preparation of the gospel of peace;
Above all, taking the shield of faith, wherewith you shall be able to quench all the fiery darts of the wicked.
And take the helmet of salvation, and the sword of the Spirit, which is the word of God: Praying always with all prayer and supplication in the Spirit, and watching thereunto with all perseverance and supplication for all saints;
The fight is a fight of faith. This is why Paul says in 1Timothy 6:12 Fight the good fight of faith, You must make sure you abide in the word of God which is abiding in God. You must know the word of God so you know what word you're standing on when you stand against the schemes of the devil. Satan's wants you to doubt God's word and disobey it. So you must know God's word and obey God's word.