finally figure out a good way to do these rocks. the silicone worked ok but after a few days in water i was able to pull it off which left a bunch of rock crumbs in the silicone so i tried putting a thin layer of epoxy on the rock then i siliconed the rock to the glass,
if anyone here thinks they have strong enough fingers to pull this apart now id like to see it and might even give you a prize, im quite shure you will be goin home with sore fingers though,
now i have to go buy some rocks that i can cut in half without to much problems,