得る、寝る as well, to give you a sample of verbs with the 〜える ending. All of these mentioned are two syllable verbs in the 辞書形, so one mora ‘in the kanji’, but this is no hard and fast rule. I usually end up correct if I assume these kinds of verbs are godan (conjugate like -u ending verbs). It helps that you often see them in conjugated form, if you encounter them in the wild, instead of learning from a list.
Strictly speaking, what makes an う-verb and what makes a る-verb is how they conjugate. The fact that you can spot them with the ~いる/~える trick is just a recongition trick, not a definition trick.
Unfortunately, the fact of the matter is, no matter how you sort the verbs, there’s always going to be exceptions - verbs that look to be in one group but are actually in the other. Golden rule in Japanese: All Rules Have Exceptions (inlcuding this one).
If you feel like just getting into things and mucking about, here’s a list of all verbs in Japanese (“class 1” = う, “class 2” = る)
I also use this rule with the okurigana as a hint, it works really well except of course for 2-mora verbs.
I also made a post about it before, here
(The only real exception apart from the short verbs I know is 交じる, which is sadly a u-verb)
I checked the list from Balthazar’s link, and apart from some verbs wrongly labeled godan (滅びる and 隠れる for example), I found 脂ぎる (possibly from 脂切る but I don’t have confirmation), 臥せる, and 抓める (all u-verbs/ godan).
Also some verbs that end in -iru/-eru that didn’t have any kanji when I checked 大辞林:
のめる, せびる, そべる, とちる