There is a flaw in the current design, where the Guard trait stops having effect as soon as the guarded unit gets its turn:

If the Hero doing Guard has its turn immediately (or shortly) before the guarded unit, then Guard is useless, because there is no chance for an enemy to strike anyway, before the guarded units next action.

Recommend: if guarded unit stays in its location, Guard should continue until the guarding hero's next turn.

This is also more logical: why would the guarder no longer be guarding, just because the guarded unit did something?