I've been chatting to the chap I bought my girls from and he gave me two new 'red mite' tips which I thought I'd pass on.
1) If you put garlic in the water don't put in whole gloves (like I've been doing), crush them first. This releases an emsyne (sp?), which stops red mite biting the chooks.
2) Wrap sticky tape (the wide type for parcels), around either end of the perch, sticky side up, so that the red mite stick to it. To remove, cut with a knife and change it every few days. I'm going to try this one today and I'll let you know how it goes.