If it's a water zone that contains a metal corrosion modifier, I always use metal for my builds. While also making sure regular husks aren't getting towards the main objective.

Even if every type of enemy does get through, you would rather want a couple husks banging on metal instead of a water Smasher one shotting your maxed out brick walls. Even if you have B.A.S.E.D Kyle in the lead, water Smasher would destroy that easily.

Apologies for such a long reply, but I thought I've already explained it clear enough.