If you're a real man, you don't need a knife. Seriously, you're worried about a dog 'mauling' you? Dogs have one weapon: their mouths. You have tons of weapons. Teeth for tearing flesh, elbows for puncturing lungs, knees for breaking bones, feet for curb stomping, and, of course, fists for pummeling that dog and reducing it to a pile of shit.
You outweigh the dog. Come to think of it, the dog probably weighs about the same as a third grader. Are you worried about a wild third grader beating you up? Get the knife if you have to, but that won't give you the ATTITUDE you need when taking on a pit bull. You have to KNOW that you're the boss with the God-given weapons.
Look forward to the fight. Dream about it. Go it there with fury. Let that damn dog bite your arm, and if he does, bite his leg. Better yet, bite it's neck.
Man up, and win.