Dogs should always be kept on a lead, regardless of how wel they behave. It is simply a matter of safety. I am not going to say that all dogs have a small attention span, but most do. I had a husky that had attention deficit "oooh shiny" and would run no matter how well behaved you "thought" he was being. Another thing that annoys me is people that dont clean up after their dogs. I have cats. So I should not be picking up dog crap from my yard! Your dog mad the mess, CLEAN IT UP!
I have cats too DM and I'd hate to go round looking for where they've messed
When we had border collie, Jess was trained to sit at roads until lead was put on or collar was held before stepping out and did that her whole life. However, a friend had two huskys which were equally trained but one got knocked over after it chased a bolting rabbit across the sand dunes and into the path of a lorry, so even the best trained dogs have moments when no training can over come instinct. Now I have young kids, I look at things slightly differently and seem to see too many untrained/over boisterous (not going to say agressive as I don't know for sure) dogs off the lead in public, my 5 year old is always asking why they haven't got muzzles on when strange dogs are running round childrens play areas.