One of the reasons why I inveterately adore the American Pitbull Terrier—and probably why most fanciers fancy them as well—is that this breed possesses the traits of gameness and tenacity at a level far above all other breeds. The pitbull, at least those that come from reputable, tested stock, will not back down from a challenge and will keep coming back for more in spite of injury or trouble to itself.
Another reason why I love "pits" is that they remind me of the tenacity and gameness required in the Christian life. The fallen world, the devil, and most especially our own remaining propensity for sin necessitate our incessant coming back to Christ. This "keep coming back for more" virtue in the Christian is called faith, and John Owen tells us that we are to "by faith ponder on this, that though you are no way able in or by yourself to get the conquest over your distemper, though you are even weary of contending, and are utterly ready to faint, yet that there is enough in Jesus Christ to yield you relief (Phil. 4:13)" and "Christ tells us that we obtain purging grace by abiding in him (John 15:3). To act faith upon the fullness that is in Christ for our supply is an eminent way of abiding in Christ, for both our insition [engraftment] and abode is by faith (Rom. 11:19-20)." 
Let the following reflections be fuel for your continued "scratching" back to Christ:
"I am a poor, weak, creature; unstable as water, I cannot excel. This corruption is too hard for me, and is at the very door of ruining my soul; and what to do I know not. My soul is becomes as parched ground, and an habitation of dragons. I have made promises and broken them; vows and engagements have been as a thing of naught. Many persuasions have I had that I had got the victory and should be delivered, but I am deceived; so that I plainly see, that without some eminent succor and assistance, I am lost, and shall be prevailed on to an utter relinquishment of God. But yet, though this be my state and condition, let the hands that hang down be lifted up, and the feeble knees be strengthened. Behold, the Lord Jesus Christ, that has all fullness of grace in his heart [John 1:16], all fullness of power in his hand [Matt. 28:18], he is able to slay all these his enemies. There is sufficient provision in him for my relief and assistance. He can take my drooping, dying soul and make me more than a conqueror [Rom. 8:37].
'Why do you say, O my soul, My way is hid from the Lord, and my judgment is passed over from my God? Have you not known, have you not heard, that the everlasting God, the Lord, the Creator of the ends of the earth, faints not, neither is weary? There is no searching of his understanding. He gives power to the faint; and to them that have no might he increases strength. Even the youths shall faint and be weary, and the young men shall utterly fall: but they that wait upon the Lord shall renew their strength; they shall mount up with wings as eagles; they shall run, and not be weary; they shall walk, and not faint' (Isa. 40:27-31).
He can make the 'dry, parched ground of my soul to become a pool, and my thirsty, barren heart as springs of water'; yea, he can make this 'habitation of dragons,' this heart, so full of abominable lusts and fiery temptations, to be a place for 'grass' and fruit to himself (Isa. 35:7)." 
 John Owen, Overcoming Sin and Temptation, eds. Kelly M. Kapic & Justin Taylor [Illinois: Crossway, 2006], 131-132).
 Ibid., 132.