Most jetski operators are pretty sensible. And jetski's don't make too much wake either.
We were "saved" by one last year, when a rented houseboat tried to anchor
on top of us, then hooked up our anchor
and took off with us in tow. The guys in the houseboat seemed to think we were chasing them, we were standing on the foredeck yelling at them to stop. Pretty sure they didn't understand english
Anyway, a guy on a nearby boat had a jetski, jumped on it and stopped the houseboat, then came round and unhooked our anchors. Have to say, 'till he intervened we weren't exactly sure how we were going to stop the houseboat driver.