And I thought I was the only one with this issue.
As far as the OP, yeah put the remote out of reach,
OR
This is more long term, unplug the box, make up something about it being too full of recordings and now it's full and won't work. You have to "fix" it, and just plug it back in the next day and delete a couple things.
Then explain to him how if he keeps recording everything, then he will break it again. Let him record a few shows, put them on auto delete after a couple episodes, in the series manager.