Outside frame 囗, but here: mouth 口, inside: old 古 (= tomb stone). [Some things like the meat of old animals or full-grown vegetable becomes hard with age.]
In the mouth old things taste: hard. [In contrast: In the mouth 口 have young things (= this is "not yet 未") a special taste 味]

Left: water 氵, right: hard, solid 固 (Many things 囗 [i.e. vegetable, roots] with age 古 get hard.)
(In respect to) the water sth. became hard/rigid, because it was dried up.

Left: metal 钅, right: hard, solid 固 (Many things 囗 [i.e. vegetable, roots] with age 古 get hard.)
As metal is hard, it can restrain.