Only bother for the needs of the visitors (food/wells) and don't waste to much money on hunters. Guards have a way better chance to catch thieves.
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Only reason to use Hunters (in the beginning) is so they can get Meat for the city, not for guard-duty since they are worse than guards at it.
Once the food desire is handled, i usually disband/fire the Hunters.
Invasions
First and foremost, to prevent getting raided by Ogres and the like, get a Temple and a Valkyrie.
Then upgrade her twice.
Her first upgrade Runes of Cunhild gives her +10 unmodified chance.
Her second upgrade is what makes her really good.
Sunrise Blessing with the temp invulnerability, making her always win the first battle each new day.
Once i have several Temples (and Valkyries) i usually disband all Huntresses AND Guards, just leaving the Valkyries as defence.
I tend to aim for at least Five Temples.
Ghosts
An Angel or a Succubus? Well to prevent annoying Ghosts, i first get a Succubus and upgrade her.
Souls consuming-upgrade makes her eat ghosts as she passes by haunted buildings.