On a average how long does a catch dog last?

Ive gotten more than a few free Pits, I always make sure they are dog and people friendly before I do anything with them. As for culling them I only had to cull one, he caught like a train but grabbed ahold of one of my female catch dogs at the house and he got the treatment all aggressive dogs get on my yard. Maybe Im just lucky, call it what you want but I believe that every pit bull out there will catch a hog if the set up is right. Its gonna have to be something special for me to buy a catch dog, the ole men I hunt with have never bought a catch dog and they have been doing this there whole lives. Everyone is gonna have there opinion, if you buy certain breeds for catchdogs and that works for you good, If the free ones work for you good. I jump on any free pit I can get and if it does what I want it stays here and I use it or it goes to a friend in need. People are always looking for catch dogs and one that catches and is free or dang near free make it even better.