If someone wants to threaten your allies, he has to get past you before that.

Prerequisites: change position, Dwarf, Off the Shelf Warforged or Sentinel

Benefit: Once per encounter as an immediate action you can swap places with a willing adjacent ally who is under attack, preventing him from being harmed, but being attacked instead. You have to succeed an initiative check versus 10 + the opponents modifier to initiative. If the attacker is making more than one attack, he may choose to attack the original target with the following attacks. You may still take a 5 foot step on your turn.