Get off my rock

The sea at Castle Cove in Dartmouth, at the mouth of the estuary, was like a boiling cauldron so we decided to find somewhere calmer to swim, and went to Warfleet Creek. This is a charming cove which leads into the estuary; the water is normally the most beautiful slatey green but today it was a thick brown. Undeterred, we set off and had a glorious time bobbing around as we headed towards the main body of the river. Then, to my left, I saw a rock which I thought would be fun to climb out onto, and maybe have a jump off. (Later I looked it up on the map; I think it's called Halftide Rock). Anyway, I was just standing up on it, and rather enjoying myself, when a man came out of a little pink house, virtually on the water, and told me the rock was his 'garden' and I should get off it. Naturally, being a polite and courteous swimmer, I did....but I did wonder how anyone can 'own' a rock in the estuary which gets covered up by the tide for quite a lot of the time...