You have to get creative. May I present, after about 10 minutes of thinking of every possible solution with things I already own, pink construction line with fishing weights attached to the end.
Yeah, I’ve been working on a new diorama. Not done yet, but it’s almost finished. Working on it in my spare time. I only started it because my neighbor gave me a bunch of free wood. This will be about 4' in width, and about 15" deep. It’s pretty big.