Bob, that "backwards learning" trick is a good one.

But no matter how well you've learned a song, your mind can still go blank momentarily during a song. (Or at least mine can.)   If you're jamming with a few folks, it's usually no biggie. You just go oobie-doobie-doo or someone else provides the line or you just laugh it off. But when you're kind of performing, even if just in a sing-around, performance anxiety can turn that momentary lapse into a full mental block.   That's where cue cards or cheat sheets can be very helpful

Oh, and another very good memorization technique is "errorless learning." Every time you make a mistake, that error kind of gets "learned" in a way, so the more often you practice something with NO errors, the more solid your learning of the correct way will be. This is another reason why it's helpful to use big-print song sheets (I recommend 20-pt or more) as helpers until you have really, really learned a song.

And are you really supposed to sing a song 100 times in private before you ever share it in a song circle or singaround, just so you won't need the 'training wheels' that first time?