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Your joey is scared and alone. He may be escaping because he's looking for another glider. He may need a friend to keep him company. Gliders are a colony animal. Some do well as a single, but require more of your time at night when he is awake and plenty of things to do. A glider safe wheels
would be a start.
It is normal for unneutered males to mark, but should get better over time. You might consider having him neutered, especially if you get a friend for him.
As far as him sleeping a lot, they can sleep up to 20 hours a day. Especially when he is stressed.
You might want to get some blankies for him( 4"×4" square fleece). Sleep with them, or put in your dirty laundry to get your scent on them, and tuck into his sleeping pouch, change out every other day. This will get him used to your scent.