Only prepare one chest and film it being burried three times.

That way you are only out $1000 and they’ll keep searching for the other 2 (non existent) chests if/when they find the chest.

This article states that they do not encrypt their group chats with E2E encryption. So they might be able to.

But it is 2,5 years old, so I am not sure about the accuracy.

https://stealthoptional.com/news/is-snapchat-encrypted-how-secure-is-snapchat-messaging/