I have some that I found at the lake last month in my sorority (Still need to get pictures of it!!) It was boiled and scrubbed and left in a 50 gallon tub to soak for 3 weeks.. and refused to sink. I got sick of it and used a zip tie to attach it to a rock and put it in the sorority a week ago. It's doing really good! All my girls love it. I did the same for some slate I got locally. The whole thing is a great effect and so far no illnesses!
A few things that link doesn't cover.
Some pieces have holes and spaces in them that a pressure washer won't clean out. Go over the whole thing with a nail and look for soft spots and cracks where gunk collects. You'll have to clean this out carefully. Not only the gunk, but any rotting wood. Basically anything soft needs to be scrubbed off.
If you find any holes that seem so small that a fish might get stuck, make it bigger with a drill or fill it in with a rock or another piece of wood. You don't want anything bad happening to your fish.
It could take 2 weeks for a piece of wood to sink.. it could take 2 months.. it could take a year. If your driftwood won't sink, you can use aquarium string (for plants), lag bolts or zip ties to attach the wood to a slag of rock, then just hide the rock under substrate. Or attach a couple of suction cups to the bottom and stick the wood to your aquarium glass. Like a lot of things in fish keeping, this is something you might have to use your imagination on.
Oh and if you use found stones, give those a good cleaning, too!