Ok so I have some large amazon swords in my 500g tank. Substrate is sand, and my catfish has been digging them up at night. My question, what can i use to keep them down? I know when they come into the lfs they have some type of metal band on them... What wouldn't harm my fish? Can i use fishing weights and some cotton thread? Im thinking like the big one ounce weights and just bury the weight. Any other ideaqs would be greatly appreciated. Thanks!