Depending on the size, you could drill out the hole and glue in a teak bung, similar to how they fill and hide screw holes on handrails. The only other thing I've done in the past is to mix up some teak sawdust or sanding dust with epoxy to create a paste and fill with that. Once you sand and varnish it is difficult to pick out the repair from any distance. You can also purchase paste/putty fillers at the hardware store, but you may have trouble getting a good color match.