What kind of ward is low-maintenance?

A dry setup is probably the simplest option if upkeep is the main issue. You could use a small dish or container with durable objects that have meaning to you, then decide whether you want to refresh the intention on a schedule. That makes it low-maintenance, not literally permanent.

I’d skip anything that can spoil or evaporate. A charm, knotwork, or a few sturdy objects kept somewhere dry gives you a similar symbolic focus without old liquid or herbs to deal with. Check that the materials won’t rust, stain, or cause a hazard where you place them.

Could also make the ward a boundary-setting ritual rather than one object that has to last forever. Pick a simple action you can repeat when needed, and pair it with ordinary practical steps for whatever you’re trying to feel protected from. That way, replacing an item isn’t a failure.