The Gaithersburg Police Station allows you to use their wall

Big wall behind Lafayette elementary in dc.

The side of any Whole Foods, Safeway, Giant, Wegmans, Kroger, Publix, Home Depot, Lowe's, Walmart, Target, any residential apartment building, any commercial building, any parking garage or anything you see that is man-made and higher than 10 feet.

Cabin John Regional Park has tennis practice walls that can be used for soccer.

Anyone knows a soccer wall in Montgomery county to practice high(not only) balls?