The effectiveness of the mint depends utterly on the determination and number of the rats! When they're in plague proportions, or starving, nothing short of an atom bomb will stop them, and I'm not sure about the atom bomb either. I think rats are a lot tougher than mice, which are definitely put off by the smell of mint, but it's like a lot of things. We mightn't like the smell of paint, but it doesn't stop us from staying in the freshly-painted house, does it? I think you'd be better to rely on the heavy-duty extermination methods.

The mint surrounding (and into) my compost bins haven't deterred whatever is raiding them one bit. Hunger is a mighty force.

I'm sure you know that you must never put meat or grease scraps in a composter... only vegetable waste and old soil..... and coffee grounds, of course.

Cant tell you about rats...I'm sure we have them but just not out of the city.
Well I've had no luck keeping mice from my pile (living in wheat field country) but gardner snakes always move in and reside within or nearby to keep them in check. Last year I had one literaly living in my cool pile all season. The only time I've seen mint work is when I've strewn it around inside cupbards/cabnits ect. to prevent mice coming in to reside in fall around wheat harvest time...the mice scatter in all directions when the combine comes thru and guess where they go! It has pretty much worn off some by early spring and I get more mice coming in. I know the numbers greatly decreased using it. What works even better is Common Tansy and since I pulled all my mint this is what I use. I got a nice huge plant from which I harvest the leaves in fall and again in spring. The smell is extremely pungent. How it would work around a compost pile I don't know, but mine is planted about 8 feet away. One thing forsure if you try this don't let flower heads go to seed or you may regret it! It's a noxious weed here so I forsure have to be diligent.

Vera

The Guinea Pig that we have does not like smell of any fresh herb that we have tried to feed it.
We have tried basil, sage , and coriander.It stays away by withdrawing its head and nose in dis-may.After few seconds it will step back and goes away at the farthest place in the cage where it will not feel the effect of the fragrance of the herb.
I do not know if this will or will not work with rats. But it will be worth-while sprinkling some cut pieces of fresh herbs around the area to see if it works with rats or not.

Planting a hot pepper in the pot will keep them away. My city neighborhood suffers from too many restaurants and not enough dumpsters, and I had a terrible problem with all my herbs until I noticed that the hot pepper plants were never touched, and nor were the herbs planted with them. Hope this helps--