Definitely doesn't work to mix feed in them. When I fed oatmeal or oats I would alternate pellet and plain oat days for that reason. If they are digging out just a single pellet or grain I know some people have made the curve of the J feeder shallower by putting a piece of hardware cloth just below the rim. They have to eat what pokes through and can't dig down into the bottom. I'm not sure how well it work or just complicates things. Mine usually gave it up after awhile with only one thing in the feeder but I didn't keep many in single standard size wire cages and they always had hay. They mess with things far less when entertained. Pellet digging doesn't seem to be a very satisfying activity if you throw them a few chewing objects, a small amount of hay, or use pens with multiple rabbits.