Oh man, Squirtle's wall cling is so GOOD for edgeguarding on stages with walls! Just jump down and press against the wall without using your DJ while you wait for the opponent to come back. Squirt can cling for a really long time, and I believe he can cling multiple times in succession. I've already utilized wall cling > wall jump bubble, fair, bair, and nair for edgeguarding already. As long as you didn't DJ before clinging, you should still have your DJ for getting back onstage (or further maneuvering offstage for the gimp), but even if you don't, if you're close enough to the wall, you can re-cling > walljump > upB.
Also, guys, take advantage of the fact that Squirtle has invincibility on his tail during bair (and f/dtilt). Because of this, I usually edgeguard with RAR bair instead of fair unless I'm already in the air facing forwards (like during a wallcling/jump).
Edit: Remembering that you can cling also lets you go really far down for gimps as long as you make sure to stay close to the stage.