One strategy I've used when there is someone behind who is obviously trying to catch me is to simply pull over and stop. If they pull over too and ask something like "need help" then you say "oh, I found it! My rear brake was rubbing against the rim but I've adjusted it now. I was wondering why I was going so slow, but now I know." If you don't want to stop just slow down a bit and pull out your mobile phone, they also won't get any satisfaction passing you when you have obviously slowed down for a reason. There are many possibilities here if you are creative.