yes i think you are right it is a derasa, and i did not pull very hard on it to make it move. but did not know if what was there was going to be a big dill to move.
as for being kept in the sand, what would make it like sand more than rock, just asking, i was told that if i had sand to put it in the rock, if i did not have sand to set it on the glass
thanks for the help