I have a 60lb 1.5 year old German Shepherd mix and she is freakishly fast. She killed a deer while hiking off leash last month. I bought an e-collar and attempted to use it to discourage chasing by giving her stim when she begins to run. Albeit I am not experienced with e-collars the highest stim did not deter her and she ran down and killed another deer. I highly recommend never alowing your dogs off leash around deer. Once they are rewarded with a chase and kill it becomes increasing difficult to prevent. In my oppinion chasing and killing is the ultimate reward and anything we can do is less desireable. Needless to say my dog will never go off leash again unless within a fenced area. I don't want her gorged to death by a buck or shot by a hunter.