I'd like to propse the idea that shouts should expire after a set time.

There are "current" shouts that are three months old, advertising horses that have long since past. I believe there have also been instances of players quitting, but their shouts just hang on the boards forever. By their very nature, it seems like a shout should be a short lived annoucement. Since they're not prohibitively expensive, anyone wishing to keep their shout up could "renew" it. 

I don't know what's fair, 1 week? 2? Would love to hear thoughts on it.