My gerbils keep scattering their “deep” bedding

I have a 40 gallon breeder and got a large bridge/wall/whatever you wanna call it to divide the tank so that they have at least 8in to burrow in half the tank, enrichment/water/etc on other side (and of course enough bedding to cover the floors, just not enough to burrow). I know they will do as they please… but I really want them to have some deep bedding! They always moving the divider and dispersing the bedding. Any tips? Should I just leave as is if that’s what they want? Should I structure it better? Sos gerbil experts! they used to easily be able to climb onto their swing for reference