Thieve's Hideout is really just another way to raid, just within each force. Here you can steal mares from other stallion's herds within the Light force. The same rules for raiding and capturing apply here, only captives switch territories instead of sides.

When stealing, post this in the subject: "I, (your name), steal (captive's name) from (lead stallion's name of captive's herd)." Then post in the captive's herd, politely, that they have been captured and must come to your territory. The highest available stallion in the captive's herd may then post here that they would like to reclaim the captive. I'll tell you if the horse remains captured or not.