First of all, it seems to me like your group is very willing to play with PVP, which is kind of unique for D&D groups. To reflect some of the other answers, this play style may or may not break your game eventually, and you may benefit from being a bit more cooperative in your games. However, it seems that you enjoy this style of play, and for that I would highly recommend playing a game of Paranoia for some over-the-top comedic backstabbing and PVP.
To actually answer your question, I would offer two solutions.
- First of all, you could invest in something expensive that fills a character-specific niche. If the other players in your group can't make use of it, they might be less likely to take a single item than a large horde of gold. Of course, they may try to sell your item, but at least watching a single item is easier than protecting all of that gold.
- If you are a heavy magic user you probably won't be asking this question, but on the off chance that you are a ranger or other applicable character, you might want to learn the spell Alarm. The spell itself is low-level, doesn't require much in materials, and should protect you without fail. You should be able to customize your alarm field to only permit yourself, and place it in a small enough area that it won't be triggered through an accident.
With that, I bid you good luck.
