I recently purchased an used pelican case with wheels. The main downside is it's rather heavy (around 20lbs empty), leaving less weight (30lbs) for the 50-lbs limit. The upside is it's REALLY sturdy. If I only had 1 checked bag, I'd probably skip this option.
I purchased it for dual-use. Specifically, when shore-diving I usually like to have a small amount of equipment on or at the shore, and want to keep it secure. I had been using a storage-tote, that I (with a cable lock) lock, which would only be as secure as someone nearby noticing a stranger trying to pry or cut through the tote. I also carry 2 keys, just in case one gets caught, falls off my harness, etc because otherwise I'd be mildly screwed if I lost my key. I also put my DAN insurance info, if I have a problem, and my contact info just incase it gets "lost."
100% Agreed with using distinct colors. However, I take it one step further, since multiple people might have the same or similar color of bag (pink, blue, green, etc). I customize my bags slightly, typically using brightly-colored tape, coth, paracord, paint-marker, etc .... something where if someone accidentally grabbed the wrong bag, it would be really obvious. "What, I didn't tie a piece of cloth to the handle!?"
I also usually have my contact info (name, email, phone) on the bag, in a place that's easy to see & secure. I usually also have a backup inside the bag as well.
If you need to save checked-luggage weight, you can also put your lead/steel weights in your carry-on luggage.