Kerry Blue Terriers have lots of energy, and need to expend it in order to be the companions extraordinaire that they can be. Kerries don't know what tired is, so the trick is to get them to relax more often than they want to!
To keep them healthy, happy, and calmer, I combine physical and mental challenges in their activities. Here are some specific suggestions, with the stamp of approval from our two Kerries.
Some Kerries love to retrieve: some love thick vinyl balls, others love those fake lambswool discs and animal shapes. Add in the command "Wait" after your Kerry knows how to retrieve. Have him "Sit" or "Down", command "Wait", throw the toy (watch the excitement mount), then release him ("Go get it!"), have him bring it back to you ("Bring it"). Add "Drop" or "Release" the toy later. Make it all fun, and then vary which commands you use so he just never knows what you'll ask of him.
Hide and Seek
If your Kerry likes retrieving, teach him "Hide and Seek" with a favorite toy. First, place the toy while he is watching, and tell him to "Find" it ("Find ball", "Find chew", etc.), guide him there, shout "Good Find!" as soon as he starts to grab it, then move back and have him "Bring it". Start hiding the object in less and less obvious places. You will be amazed at how fast your Kerry has learned the name of an object, if you always refer to it with the same name.
Kerries are very smart, and will generalize the concept of one activity to another. For instance, I actually have Lady herding Tyrone into the house when he has been out too long, by telling her, "Find Tyrone". Out she goes, sticks her face in his, sometimes with a quick bark, and in the two of them come.
I also get her to bring in the many, many toys that accrue in the yard over a day or two by telling her to "Find ball/mousie/chew" whatever (one at a time) until they are all in the house! I can also tell her to go find her ball in the house when I need her out from under my feet, knowing that she'll have to really look around. She often remembers where she left the object and goes directly to it. She'll go upstairs looking, too. When she comes down with a dirty sock, I know it is laundry time.
Another mind/body activity that Tyrone (who will not retrieve) likes allot is "Smell It!" He lies down in the kitchen on his rug while I'm working or cooking, and I put things in front of his nose and say "Smell it!" This may sound like a very passive activity, but it is not if your Kerry tends to smell everything in the environment, as Tyrone does. When I'm out and away from him, I'll purposely make contact with a friend's dog or cat by brushing knee-level and patting them; smelling me keeps Tyrone busy on and off for hours after I come home! (Of course, I have to endure his looks of disgust that say, "Where have you been, and with whom, without me? Harrumph!") He reacts to whatever he is smelling in many ways: His eyes open wide at a new smell, he'll snort at a smell he finds unusual.
Sometimes, having a good, hard bone to chew at relieves a lot of energy, especially if they have been excited by some activity that had to stop. Use Nylabones, Plaque Attackers, sterilized bones, not lightweight chewies (I hate hooves, etc., especially what they do to Kerry beards.)
Any kind of training, whether formal obedience or just good manners on leash is good for Kerries, but incorporating them into daily walks, to keep them thinking and pleasing you, is better than just a walk. Walk fast for a while for that enjoyment and release of some energy, then ask him to "Heel", "Stay", etc., then walk fast again ("Let's go! Oh boy, oh boy!"). Don't forget to stop and "Smell" the roses (and phone poles, and...), too!
Finally, when all else fails, when the weather is horrible, or it is late at night, is the game called "Stairs!". Tyrone invented this as a game from our attempts to teach him "Come", but Lady learned it quickly, and likes it, too. One person is upstairs, the other down. Call your dog, "Come on, Tyrone! Stairs!" Be really excited, clap your hands, etc., to get the dog all excited. Every time the dog emerges from the stairs, be in another room or half-hiding behind a door or whatever. Then tell the other person to call the dog, and he/she does the same thing. Get really excited, too, when the dog comes up to you (they must come up to you, although, in this game, I don't make them sit to finish, plus their tails are wagging too hard for their butts to make contact with the floor!) Better than a StairMaster, our Kerries love this and will run up and down at least 10 times each way before they want to quit. (Note: They want to quit! Ah, success.)
We also have a shorter, more boring version of this in the yard, one person here and one person way over there, but nothing beats "Stairs!"
I think the key to whatever you decide to do is to engage the interest of the Kerry by being really excited yourself, and use their minds during most of the games. Although stubborn at times, they are quick learners. After a good game where both you and your Kerry had a lot of fun, nothing is better than a tired-out, happy Kerry at your feet!