If your creation is a sitter of some sort and requires some weigh use pellets, marbles, plastic beads or glass stones, .Think twice before using beans or rice, when they become wet, sprout. To keep them in place, you can use a knee-high nylon stocking and put the weighted bits inside of that. Tie it, so it makes a sack. You don't want it to be all floppy. Do not put them directly on the bottom. Put a small bit of stuffing in first, then the weighted stocking sack, then more stuffing.