>You could buy bear spray

No, you cannot. Bear spray is illegal in DC and any populated area. I assume you've never used bear spray (I have several times). It is not something you want to use. 50% of the time the mist will come toward you or toward other people, thus placing their health in serious danger.

The OP can use mace, but record the entire incident because in DC you can be charged with assault with mace unless you can prove it was for protection.