I have two Kirilian bear dogs and it depends on the time of year if and when I let my dogs run loose, if its winter time and snow on the ground I' ll them run loose with me but dureing spring dureing birthing season for the deer/elk and other critters I walk my dogs on a leash or they will stay inside or outside in a pen, but my dogs have a killer instinct also, not too sure about your breed of dog, but I think yours may be more mellowed out as opposed to mine. I know there are some breeds that would not feel bothered by deer, but then again you have a breed like mine and you treat it as such, so I am sure there is only one way to find out is turn him loose and find out and if he drives the deer away, then make changes as the deer will always come back in time, good luck and let us know the results, Bobby