In the boat I have now I have 2 pucks mounted using velcro. They seem to be holding up ok. I’ve only been on the water a few times with the puck I mounted this year. The other GPS was mounted by the previous owner of the boat and it is holding up good. I haven’t noticed any problems with it, but I am not sure how long he had it mounted there.
In my last 2 boats I had the puck mounted on a gimble mount, just like the ones most marine radio antennas are on. I put 2-#10 screws in it and it held fine. I had it mounted on a carpeted surface and when it was removed it was hardly noticeable once the carpet was ruffed back up.
Josh