Good tips.

One other step ... staple the check to the signed letter stating ... by accepting the refund, signing and cashing the check ... he agrees to return the membership card and remain off private property. And anything else pertaining to your bylaws.

The signature on the back of the check becomes signature for the "contract", in this case the letter. Photocopy the check stapled to the letter before you send it certified mail. If you want to really bat it home, write in the notes in fine print "Cashing of this check constitutes your acceptance of our restricted agreement".

This kind of an agreement is call "restrictive endorsement". A legal contract in most states, better than nothing in the rest.