Agree with the pepper spray. Also, carry a loud whistle or a pocket alarm on your key chain. You can get these things on Amazon.

Don't make yourself ugly. But don't be provocative either.

Perverts don't care if you are attractive, recently there was a sexual assault on an elderly woman at the Quincy T-stop.

If anyone approaches you, keep your distance and ignore them.

Eta: Don't know anything specifically about Natick. But bad things can happen anywhere. Stay in well lighted areas and where there are other people walking around.