Your hero will earn the guild loyalty rank of CHIEF MASTER once they have remained in the same guild for 35 consecutive calendar days. The rank of Chief Master is the highest ranking possible where your hero will still randomly start a quest to leave their current guild. Your hero will need to acquire the next level in guild loyalty in order to no longer search for and join other guilds on their own, with one exception: If a god does not check on their hero for over 28 days, they will leave the guild regardless of their current rank.
To force your hero to stay in the guild, send a voice message such as: abandon your quest or this quest is dumb. Stop doing it!. It may take more than one send in order for your hero to listen, depending on a complex formula which includes: how long they have been in the guild times how many people are in the guild divided by their attention span.