How do you approach a neighbor..

[Justin B.]

I purcahesd a duplex last fall and we noticed the neighbor has a large amount of dirt leaning up against the back of our garage which is starting to rot the wood of the garage. 

I talked to him previously about its effects and he wanted me to move the dirt or pay for it. I dont feel I should have to pay for this and I want him to remediate the situation.

What's the best way going about this to have him get this done?