the leash part is new

In all the times we have been stopped on the beach with our dog, not once has the need for a leash ever been mentioned. Until yesterday. I think this particular doggie cop just needed to assert his authority over us in some way. Since he already knew we had a permit, there was only one thing left for him to say. About a month ago, when he demanded to see and was shown our permit, he then told us we needed to give him a copy of the permit. That was the last time we had seen him until yesterday. And then nothing about giving him a copy (which he obviously did not need) but instead this business about the leash. I must add that not all of them are like this. Some have become quite friendly with us. I am puzzled as to why there are so many, and why they change so frequently.