Behind my garage, there is a small strip between the back of the garage and my neighbor’s fence. The problem is that the soil is sloped toward my garage, and if I dig out the soil to slope it away from the garage, it would leave a 12” gap under the fence, and they and I both have big dogs who would love to kill each other. The strip is about 22' x 40". Half of it is covered with corrugated polycarbonate, with a gutter and an awkward downspout that I currently have emptying into a big trash bin but it's a pain to empty, yet I don't have good options for draining it elsewhere. Any suggestions?

Even better if I could turn it into usable storage space.