An effective mouse deterrent is one that repels mice without significantly impacting to your day to day life. It should not require you to alter your way of life so much so that you forget the way it used to be in the good old days - before fighting mice became a way of life. Idealling a good mice repellent will work naturally and will not have overly harsh chemicals that burn through the affected area.
Keeping those ideals in mind, that is why I most recommend Shake Away Rodent Repellent. I don't generally attach a highly recommend to any product, but this one satisfies all of our requirements and more. It is a granule based product that works by exploiting a rodent's instinctive fear of its natural predators. The product is granulized fox and bobcat urine - the scent acts as a mouse deterrent as they believe their predators are nearby. Additionally it's 100% organic and will not burn plants, trees, or bushes. Simply spread the product all around your house, or in your garden, or your barn, or around your shed, and consider your mice problem eliminated. It's an effective way to get rid of mice naturally.
Another effective mouse repellent is to use one of the ultrasonic repellent devices available on the market. This is more for indoor use whereas the Shake Away described above is more effective for outdoor use. An ultrasonic repellent works by emitting a high frequency sound that proves to be extremely irritating to rodents, but cannot be heard by humans or common household pets like cats and dogs. Note that if you have a rodent pet (hamster, gerbil, etc...) do NOT use an electronic repellent device as this will cause extreme discomfort for your pet. When looking for an ultrasonic repellent, you want to find one that employs non-repetitive sound waves. That is, the sound emitted varies with time randomly so that the rodents are unable to become accustomed to the pitch. We don't want them getting used to the sound and hanging around, so the variability is important. Also it would be nice to have a sound that mimics other mice, in particular the alpha male rodent. The alpha males are extremely territorial, so by emitting a high pitch simulated alpha male sound in addition to the non-repetitive sound, it's a sort of one two punch to deter mice. One product to try is the Victor® Mini PestChaser® Ultrasonic Rodent Repellent. It exhibits the qualities I described.
Something to be cognizant of is that ultrasonic repellents have to be properly placed. If you put it behind furniture, it won't work because the furniture will simply absorb the sound. Similarly, if you put it in a huge room, the sound diminishes in which case you should try and find a more powerful unit. Don't expect to put an ultrasonic repellent in one room and expect your entire house to be rodent free. You need to place one or more ultrasonic repeller in EVERY room of your house to keep the rodents away. Also as with any anti-mice campaign, you should still deploy traps for a multi-pronged approach to get rid of mice. As a matter of fact, these ultrasonic repellents can be used to herd mice away from certain rooms and towards the rooms that have a bunch of mouse traps deployed. Keep these helpful tips in mind.