Plenty of outboard locks available, from simple cables and padlocks, to crazy bars that cover the clamp handles. You'll find plenty if you google outboard lock. The trick is finding one that fits with your outboard mount bracket. On a 23, you probably have a lifting Garelick type, which ought to allow any width bar style. They don't often fit on smaller fixed position brackets where the clamp screws are down between the side pieces of the mount bracket.
Brian