Thanks for posting! What a tricky dilemma! I think Dana’s chalk trick could work really well to fill up the holes that you’re not able to cover with wall art. If you’re looking to cover an entire wall, a tapestry could be an easy, large-scale solution!
As far as hanging art without making holes, I fully support Command strips and hooks! I decorated three dorm rooms in our studio last year, only using command strips and washi tape to hang art on the walls!
Hope these tricks and tips help! Good luck with your rental!