It is very dangerous.... to burglars and boys who want to retrieve a ball from the garden. The cats have no problem whatsoever in navigating the wire. The only danger is a cat collar getting hooked behind it (or behind a branch, of whatever). Which is why my cats no longer wear collars. They open their cat flap with their identification chips.
Nearly everyone in the neighbourhood knows them, anyway, especially Catweazle, whose face is in the community paper every 2 months. He is our 'stealthy reporter' and writes his own column, which he dictates to me.