18 is wild, so I would assume 16 or 18 wis guards proficient in perception, by level 17 would get +10 without any other kind of modifiers.
If they are rogue guards with 14 wisdom they get to +10 by level 4 with expertise. Again, if the DM is handling stuff to get them get to +18 I’d assume he can make guards get +10 too.
18 is wild, so I would assume 16 or 18 wis guards proficient in perception, by level 17 would get +10 without any other kind of modifiers.
If they are rogue guards with 14 wisdom they get to +10 by level 4 with expertise. Again, if the DM is handling stuff to get them get to +18 I’d assume he can make guards get +10 too.