Is there a trick to wet sanding

[smurfmeister]

I tried to sand off some marks on my gelcoat this year. I purchased 1000 grit paper and when I wet it and sanded the area in question it didn't really remove the mark but actually created an area that now stood out from the rest (like it had been sanded - which it had). I compounded it and it seemed to help but it scared me off from going any further.