Anubias & java ferns are attached to the rock--sometimes you can wedge them into a niche, others use fishing line or cotton thread to tie the plant gently to the wood or rock. After about a month, the plant will be attached to the object (in most cases--I have one anubias that after one year, and lots of growth, still refuses to attach).
For a bottom feeder--cories are nice, and there are a wide variety to choose from. A trio of them will be happy, and the shark shouldn't bug them other than to keep them away from his cave. Dwarf puffers can nip their fins though, so you have to be careful. I would avoid most loaches, as they will compete with the puffers for snails, but kuhli loaches are a long time favorite of mine that do well with puffers. They prefer to be in groups, and while not as active as many fish, they are very fun to watch when they are out.
Visual breaks = decoration or plants that break up the tank area, so you can't see all the way through, front to back or side to side. If there are lots of plants, wood, and such, the puffers can get away from each other, and this will reduce aggression.
For a bottom feeder--cories are nice, and there are a wide variety to choose from. A trio of them will be happy, and the shark shouldn't bug them other than to keep them away from his cave. Dwarf puffers can nip their fins though, so you have to be careful. I would avoid most loaches, as they will compete with the puffers for snails, but kuhli loaches are a long time favorite of mine that do well with puffers. They prefer to be in groups, and while not as active as many fish, they are very fun to watch when they are out.
Visual breaks = decoration or plants that break up the tank area, so you can't see all the way through, front to back or side to side. If there are lots of plants, wood, and such, the puffers can get away from each other, and this will reduce aggression.