Can I play Retreat in response to my own Retreat to get 2 exhausted runes?

Ruling: No, this does not work. When the first Retreat resolves (last on the stack), it cannot find the owner anymore, so you don't channel the 1 rune.

Sequence:

• Play first Retreat
• Play second Retreat in response
• Second Retreat resolves first, returns the unit
• First Retreat resolves, but cannot find the unit to return, so no rune is channeled