Ah. Well. I have about sixteen long plastic tubes about eight feet long, which when full probably run between 60-80 pounds. We intend to get a safety fence, but we positively cannot afford it yet. And while I've trained my dogs to come when called, stop barking at neighbors, not jump on people, not chew on furniture or anything in the house, not beg, not chew on the pool toys and a lot of other things - I haven't succeeded in getting them not to chew on something that looks exactly like a big rubber chew toy in the two days they've seen them. Teaching them is a priority, but I'm only home three hours a day, and they can destroy the lot if they want to before they've learned it. I just need something to prevent that from happening that I can afford in the next week. This seems to be the simplest short term solution.
What I don't know is where people buy large quantities of sand - gravel pits, etc, for landscaping.