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They do slide around a bit, what I do is glue either lolly sticks or dowels onto the shelf leaving enough space for the wheel base between plus a little extra so it's not too tight a fit (if the wheel isn't on a wooden shelf you can just do the same with a piece of card but it may not work so well) then I put some toilet tissue under the wheel base, a few sheets in length folded in half is just the right size, Zen always used to try to pull the tissue out & almost topple the wheel over on top of her so that's something to watch out for but the boys have all been fine with theirs.