The plastic owl seems ubiquitous, and as the linked photos showed they can become perches for gulls.
I have friends who used long plastic snakes (toy snakes) and they say they worked.
On my art gallery building, above the front door and front windows, there was a ledge that was perfect for pigeons and they can poop like gulls.
This is what was installed on the building ledge and around the signs and my neighbors (commercial buildings) used these too. They worked very effectively to prevent birds from landing there. The are made of plastic or steel
(galvanized I believe) and maybe you can find some in SS. This would be what I would put on top of radar
dome (plastic version).
I would also consider buying
these as long strips, and use some industrial velcro to attach to boat while gone, remove before leaving the slip. Or use something else to keep them upright on long surfaces. Easy on and easy off.
Defender Anti-Roosting Pigeon Spikes - PCRC
Some people use CDs on monofilament fishing
line that is attached to lifelines
. The reflective surfaces swing in the wind
. It was recommended to use a "swivel" (like used for fishing
lures/hooks) to allow the CD to rotate freely.