We always use our Tennessee Mountain Curr named Patches. We didn't have to train her to tree a squirrle, she just does it because that is what her breed is designed to do. She is also a born killer, so we have to get to the squirrles before she does. On her own she has killed at least one of the following: squirrle, rabbit, opposum, ground hog, mole, chipmunk, and mouse. If it moves she pounces on it. Once whatever she has stops moving she stops playing.