Instead of using poison to get rid of the mice making a home under your walkway, use a trap that you can set with a bit of food. Just set it out and check it once or twice a day. You can either use a traditional trap that kills the mice (though you'd have to deal with the dead mice) or a humane trap that captures the mice without hurting them. Just be sure to take the mice a decent distance away to free them, like a local park or patch of woods, since they'll run right back to where they were if you just let them out in your back yard. You can pick up either kind of trap at a hardware store. But, really, you might just want to leave them in peace and count your blessings: at least they aren't inside your house!

If you are fond of pets get yourself a cute cat. This will help.

I live in a major city, so no matter how clean you live- you are going to have a mouse problem at some time or another.  I have found THE BEST way to get rid of pesty rodents (exterminator approved!!!). 

What you do is by poison pellots, any kind, and instead of just using them as they come, you put some in a zip-lock bag and pour a little bit of peanut oil into the bag- just enough to coat the pellets but not over saturate them.  Zip the bag up and shake it until the pellets are pretty much covered with the peanut oil.

To make sure that the mice are eating the pellets and/or how much they are eating, you can take the lid of a water bottle or something similar, and put a certain number ( ex. 10) in each lid.  Put them around where the mice are most likely to come in contact with them and in a day or two, check to see how many pellets are there.

The reason why this works so well is mice can begin to recognize poison, but with the peanut oil, they think it is food.  They actually take the poison BACK to where ever they are "nesting" and the other mice (if there are more then one) will eat the poison too!!

It is BY FAR the most effective method I have ever tried or heard of to get rid of mice.  Try it and I promise,  it will work!!!