3 Answers

You will never win.They are persistant little buggers. I know some commercial fishermen sprinkle the dock with caustic soda so that it burns their feet.I'm not suggesting you do that,it's a bit extreme.But perhaps you could come up with something less harmful to sprinkle around.

Make sure there is absolutely no food source around the dock.

I know that boat owners drive nails into dock pylons and cut off the heads afterwards to keep Seagulls off them, but a dock itself is a tough one.

Some of them mount PLASTIC OWLS nearby.

Do not fish on the dock, or leave bait. Do not allow anyone to feed the birds on the dock. Take food to another area to feed them. If the  community is posted a bird sanctuary you can face a fine if you harm one.  You need to check with the department of wildlife. You can also call the city and check on possible bird sanctuary.