If you avoid using a name that was mentioned somewhere else, then eventually you can't use anything. Parth Galen wasn't a major location in LOTR, so I wouldn't worry. If on the other hand, your main town was Bree or Dree, and you had a castle named Delm's Deep, then I would worry a little more.

I have found that names that I used, that I thought were pretty unique, ended up being some obscure character from the Silmarillion, or one of the unfinished tales or something.