NHF – new heroes for Heroes V 3.1.

You could display a window with a question:
"This object is guarded.
Hamsters: Horde
Hamster Berserkers: Many
Are you ready to fight them?"

Added 1 minute ago
Yes, and you can spend not only money, but also other resources, turns, mana, etc., on guarding.

At least it's not very beautiful, but it's possible. However, this will also reveal the opponent's hero.
And if this ability is implemented as a skill, it will be interesting.

Added 2 minutes ago
I would also like to add the ability to establish dwellings on the map as a separate skill.
It could even form an entire branch in the leadership skill tree.

Added 6 minutes ago
In the old mod, there was the possibility to upgrade mines so that they would extract more resources; the possibility of populating mines with creatures has been discussed for several years now. So, if these two possibilities cannot be simply included in the mod? Without any skills, but just by asking: "Do we want to hire guards?".