Volvo 290 stern leg astern lock

I have a permanently moored launch and have a problem with the stern drive lifting up when put in astern. The lock or latch mechanism that retains the leg is not working due to marine growth accumulating around the latching system. The antifouling paints do not appear to be anywhere near as effective as they used to be as after about 6 months from antifouling this problem starts to appear. I can't really see any real reason why one couldn't have the leg locked in position permanently so that this potentially embarrassing problem can't occur. Just wondering if anyone has had a similar experience and has found some simple way to lock the leg down.

Appreciate any input.

Cheers
Colin

What antifoul are you using?

I have tried numerous brands that are suitable for alloy stern drives, none of them seem any better than others. In the last 2 to 3 years there has been a substantial increase in marine fouling especially barnacles in our area. The entire hull is affected not just the stern drives but it doesn't take a lot of fouling to make the latching of the stern drive unreliable. I have a small runabout as well and there is no system on the outboard motor to latch or unlatch the drive.

Cheers
Colin

Have you tried using prop speed instead of antifoul? Even just try Prop Speeding that area maybe. Burnsco stock it for self application now. I guess you have tried Trilux, Hempel, and Petit Vivid? They seem to be the commonly available antifouls and as you say there isn't much between them. Maybe the PV slightly better.