I think often times any extra noise made can cause them to break. I want a catch dog to lead on a loos lead if possible. I also believe a catch dog that can pick and choose the route they approach the hog, instead of one that just goes wide open breaking brush, will catch more hogs. I try to approach from down wind if possible.
X 2 I had a buddy who had a pit who picked his way thru & I dont believe that dog ever missed a hog.
Myself, most of the pits I have had go full bore & it stands to reason they make more noise going in which can cause a hog to break & also in thick cover, they can miss, even the good ones.