Thanks for hte reply. How tacky is it? I tryed the the Great Stuff last night but its not sticky or thick as I thought it would be. Is that stuff thick enough to hold rubbel?

Not vertically. Basically what i did was laid the overflow on it's side and did one side at a time. As for being sticky, I strongly recommend you wear plastic gloves. This does adhere to everything and was a bitch to get off my hands. Once it expanded for a few minutes, I just threw on the rubble followed by some sand. Worked well.
Are you building a back wall?

Thanks. I have 2 colums built with PVC, and an arch connecting the two with larger rubbel zip tied on to it. What im trying to do is fill the gaps and stick rubbel on. The arch has a hole in the middle that im trying to keep there. I might have to foam in the gaps then drill it and use rod and silicone to finish. I cant find my camera charger battery otherwise I would throw up some pics. Hope that makes sense.