I've discovered that a near neighbour likes squirrels and is feeding them, hence the huge population of large greys. I don't have the "greys vs reds" prejudice which some people do, but I am concerned about the "large greys vs cats" issue, and I'm worried by what Slugsta has said. I'm not exagerating in saying that there are dozens of squirrels who are double the size of most rats. There is a tree in my garden which has no bark....I wonder if it's been stripped.
My cats are all ex-ferals and I'm concerned that they may attempt to chase the squirrels and get badly hurt. Unfortunately, every time I attempt to put a collar on them - quick-release - they think I'm going to strangle them and run off! A collar and bell might help to prevent a confrontation, perhaps.