I've heard that using a laser beam or a flashlight to exercise your JRT is NOT a good idea. Is this true?
Yes, it's true.
The Jack Russell Terrier is an earthworking breed. This means that their very nature is centered around hunting. What makes this terrier so alert and bright is the fact that they're ready for anything to come their way; after all, it takes a bold, highly intelligent dog to find his way through the earth to either bolt or keep a fox at bay. A fox is a treacherous enemy for any dog not equipped for the confrontation both mentally and physically.
When a Jack Russell Terrier does his/her job in the earth, he/she needs the senses of sight, scent and sound... not one or the other, but all of the above. Imagine taking all those keen senses and limiting them to sight only. Basically, that's what allowing a dog to hunt a beam of light is doing. The effect this will have on a terrier will be one of confusion. VERY rarely can a terrier fully understand that the beam of light comes from a flashlight or laser light alone, and more often than not, they begin to think they see the light when their owner isn't even holding the mechanism that creates it. When this happens, the owner has succeeded in causing Obsessive Compulsive Disorder (OCD) in their dog.
Can you just imagine how confusing it is to a dog that something that attracts your sense of sight is so unexpected that you can't smell it, taste it, hear it, or otherwise sense it?
Can you just imagine how confusing it is to a dog that something that attracts your sense of sight is so unexpected that you can't smell it, taste it, hear it, or otherwise sense it? It's just this phenomenon you SEE, but cannot sense in any other way. The dog will begin chasing things around the house like the flash of car headlights coming through a window, or even the glint of light off a watch. I had a rescue once who could absolutely not ride in a car at night because the shadows created by oncoming car headlights sent him into a total tizzy, as he tried to chase the shadows. Sadly, he was given up because his own owners created OCD in him that they just couldn't deal with any longer. This happens more often than you'd think. Owners are not being cruel; they simply have no idea what they're creating with this game.
There's a great chapter on this in Nicolas Dodman's book The Dog Who Loved Too Much. It's titled "Chasing Rabbits," and tells of a Bassett Hound who was given up because of the OCD caused by chasing a flashlight beam. Caroline Coile also addresses the topic in her latest book, Jack Russell Terriers Complete Owners Manual.
By all means, if you need to exercise your dog, try to find a way to do it without using a flashlight or laser beam.