What to do when your dog steals and buries anything he can grab?

So lately it’s been a more intense issue. I have a dog, 6 year old border collie blue heeler mix. His names Remy. Never was this an issue up until a couple of months ago. He has stolen and buried important medication which I only found recently when digging in and leveling out my backyard. he steals clothing, or really anything that he can when you’re not paying attention and either buried it or takes it outside into the mud. He has toys, we give him things to do. Not sure where this behavior came from. tips are appreciated. Thank you. He’s a dork and I love him but stealing clothing and medication is a big issue.