safe for betta

Hi all! I'm new to these forums and relatively new betta owner (I had a betta about 10 years ago who lived about 4 years, and I finally worked up the nerve to get a new one - knowing a lot more about proper betta care and general aquarist knowledge than I did back then, but definitely still...

Petsmart has a bunch of nice stones and rocks, but they're pretty expensive. I really don't see anything special about their "betta rocks." So, is it alright to use stones (smooth ones) from outside in a betta tank? If so, what is the best way to clean them to eliminate bacteria but keep them...