When we lived in Fort Collins CO we had a big beautiful dog park built, lake & all. Space for small & large dogs separated by fencing. What we found out is that some dog owners would leave their dogs & go shopping then return to pick up their dogs. This happened for quite awhile until a puppy got killed and the killer's owner wasn't there. The cat was out of the bag so to speak. So now everyone is aware and looking out for this not to happen.