RATTLER! Wow, I'm impressed! Had a copperhead on mine last year. Must have been in anchor well as I went to bow, then back to cockpit for some tool, then back to bow. Did not see it on first trip to bow. Wife has gotten in habit of stomping on anchor locker before we leave the dock. She's be taking a swim if it made an appearance after we left the dock.
No suggestions as to how to keep them off...