Locktight should do it but what usually causes it in our area during winter is that most people just don't break the wipers loose when they're frozen by ice to the glass and/or use the wipers to plow off heavy snow and they can't take that. Sometimes the left wiper arm also gets bent and then it doesn't contact the glass fully, can be bent back easily.

If people just loosen the frozen blades and use a snow brush instead before turning the wipers on, that nut wouldn't keep loosening as it never happens here in summer.