my friend makes these and uses a heavy tile instead of sand! I like it much better and it never moves

I use rice for the pincushion and put the rubber shelf liner on the underside. It holds onto the table very well.

you can use rice or beans, anything heavy.. tiny pebles, glass chips (smooth)

Here's another idea... "poly pellets." They are washable, and mold to the shape of whatever they sit on. I usually buy them at Michaels. I've also used crushed walnut shells and wheat, but I like the poly pellets best.