Not sure if wire mesh will slow them down... I have heard that they carry bolt-cutters when they're on a mission. Oh, sure, they look all cute and Disney-like, but they can be nasty.
At Bell Harbor Marina in Seattle, we were in our boat, when it felt like two big guys jumped on the cabin-top. I sprang into the cockpit and found myself looking at two river otters - they were in the dinghy on top of our boat. Knowing what they would leave behind if I didn't get rid of them in a hurry, I raised my arms up (to look bigger) and made a sharp growling noise (that apparently works with bears)... one of them pulled a switchblade and the other said, "Bring it on, human!"
You know that old saying: they are more afraid of you than you are of them? Not true. It might be because there were obviously street-smart river otters. I grabbed a long handled brush in the cockpit, ready to defend my wife and cat - who were both at the cabin door, saying, "Get 'em!" Pretty sure they were talking to me, about the otters, and not the other way around.
The otters laughed at me, jumped off our boat, and onto the boat across the dock from ours. Close enough. Within seconds, they unleashed some particularly offensive smelling excrement. Sorry for the owner of the other boat, but I dodged a smelly bullet. Not to mention the potential for rabies, or scabies, or some venereal disease those critters likely had.
This probably isn't any help at all. Sorry if that was your boat they got on after they left mine. Just kidding - this true story was years ago... and the otters haven't become any better behaved. Maybe put a wolverine in the cockpit?
I like the metal mesh idea. Good luck.