I do try to avoid being by myself, so I don't usually get into situations when I am alone with a guy I don't know or anything like that.
But of course, I can feel concerned about it every now and then, since I notice guys of all ages looking at me, and most of them are much taller and bigger than me, so I don't really have any confidence in physical defense either, unless maybe I try some self-defense class or something like that.
But it isn't really something that worries me that much, unless I end up alone with a guy that I don't know, but this is very rare.
It might happen if I go to the gym in the mornings, but the few guys who go there during those times have always been very respectful to me, and never given me any bad vibes at all;
they are generally busy with their own things, and basically say "hi" when they meet me, so I am fine with them.
Also, there are usually janitors and other people who work there, so there is that added sense of safety as well.