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They might find a ground/wall anchor a bit more agreeable, takes up a lot less space and only needs a couple of holes filled in if they remove it once you've gone. Most ground anchors and bike racks require 'permanent' bolts (usually just a ball bearing hammered into the top) to stop thieves just unscrewing them, which might also be putting your landlord off. They aren't actually permanent, but certainly are a pain to remove.
Some make use of the lock itself to block access to the screws, meaning you can use easily removable ones instead. The hiplok anchor is easily removed and far from unsightly.
I think these look good. Somebody could get it off with a prybar I think but it would take a bit of work. They have a smaller one that's like $25 Bud I don't know anything about it, I've only seen the bigger ones. Probably the same with a smaller mechanism to lock into.