Quail crisis!

Bit of a traumatic day today - two of our quails were attacked and killed in the night.  We have no idea how anything could have got into the run.  We assume it was a rat.  Since we don't know how it got in we don't know how to keep it out, so now we have three quails in the conservatory!  Our poor quails seem to have been facing calamity after calamity over the past few weeks.  We've had a couple lost to rat attacks recently - we tried to reinforce the run but obviously we're missing something.  Then one of Rhiannon's baby quails died of some infection a few weeks back.  I think poor Rhiannon is feeling a bit defeated.  She does everything she can to look after her quails as far as I can see.  Things just aren't going too well at the moment.  Not really sure where we go from here.