Instructions
Find a mercenary or bodyguard that you want to hire. There should be at least two in every major city in the first "Fable" game, including the assassins in the bandit camp, the paladins at the Temple of Good and regular fighters scattered throughout many of the other towns. Pay the fee and hire the guard.
Hero save once you've started a quest with your bodyguard. Hero saving is a flawed mechanic in "Fable," and if you're in the midst of a quest, it will often reset your possessions and treasures, allowing you to get more than one of a single thing. You may need to accept the quest first and then leave to hire a bodyguard in the middle of it so that when you save, you still have the original guard and a new one has spawned. It isn't guaranteed, but this glitch often works for duplicating quests and quest items.
Get your bodyguard killed. If you simply want to use a bodyguard until he gets himself killed in the line of duty, he will respawn after 1 in the game day in the same place he was when you first hired him. If you need to kill time in the interim, go to one of your houses that you've purchased or an inn and sleep for a while. He'll be back very soon.