Prepare a stock pot with simmering water and dish washing soap or laundry detergent. I have long tanks on gas burners for this purpose, however you can make do with a plastic planter into which you have poured a solution of detergent and boiling water. This serves two purposes. This swelling will minimize dents. Be careful not to scald yourself.
Gloves are useful.
Aggressively scrubbing the wood with a toothbrush will help. Usually a half hour is enough. I put a heavy object in the pot to keep the stock submerged. For stocks slightly longer than the stock pot, simply invert half-way through. Another technique is to spray down with Easy-Off or other oven cleaners.