Depends alot on how big the pieces are some of the larger ones takes months to sink. I just about went crazy trying to get a 3' long by 7" tall to sink the last few weeks. I ended up screwing a 3 foot rubber maid lid to the bottom and burying the lid under the sand and it barley stays down.
zip tie it to a piece of slate. Drill holes on both the wood and slate and position it the way you want and it should sink. Thats what i have been doing.
i think i will try silicone, i work at a place with alot of quad / silicone, wondering if something like geocile or OSI quad or hm270 will work... Aquarium silacone is spendy at my lps
yea thanks lol, i guess ill figure it out might have to go with aquarium silacone if that method works well? other wise i guess can go with the rock idea