[Gerty333]

Argh! I just saw a rat scurrying down the side of the chicken coop!! What do I do?

[bantam novice]

Several options.  I have a Jack Russell Terrier that keeps rats at bay.  I have seen eradibait recommended.  Some people say a humane trap then release far away from the hens.  I'm sure someone more experienced will be able to add a little more detail to this.
Generally make sure that chicken feed is stored out of rat reach at night (I use a galvanised metal bin with a secure lid) and that the chicken coop is rat-proof (weld mesh rather than chicken wire).  Keep your eye open for the little digs and holes that they leave.

[leddenton]

I had a rat problem last yr but it was made worse as I had left it too long before realising I had a rats! We laid a trap best bait we found was peanut butter! You may have to leave it a while open so they become confident using it as a through run then set it.We did erradicate them using this way, eventually!

[joyfull]

once trapped and caught you should not release them but cull them as quickly and humanely as possible.
You will have always had rats about but they will become bolder as they can smell the feed 

[Gerty333]

thanks for the advice!! i'll be setting some traps and checking the coop today then!

[Kate and her Ducks]

once trapped and caught you should not release them but cull them as quickly and humanely as possible.
You will have always had rats about but they will become bolder as they can smell the feed 

Agree with this. You are not permitted to release vermin once trapped, they must be killed. Releasing them elsewhere just leaves the problem to someone else too.

I also had a rat problem at my last place and was difficult to sort out once established. |Had some success with eradibate but in the end found trapping and killing more successful. AM much more vigilant now but we have a large population of feral cats round us and I think this accounts for much of the fact that I have seen no evidence of rodents here.