How to get stain out?

[button+banjo]

So my bunnies (although they are litter box trained) decided to randomly pee on their new Small Pet Select hay feeder. Since they live outside on the porch it could have been for a number of reasons. It sits on the ground and is made out of untreated pine wood. I soaked the area in Seventh Generation cleaner, but the stain remains. Does anyone know how to get pee stains out of wood?

 

[button+banjo]

Anybody?

 

[Blue eyes]

I know that plain vinegar can dissolve the white chalky residue that urine leaves behind. However I don't know how it will do on wood.