We've dealt with (are dealing with) this BIG time in Lucy. She is extremely reactive to motion, which is a major problem in agility when you have to walk out to the start line while another dog is still running the course. Our runs are MUCH prettier when it's a calm, collected dog before us vs. a super drivey one with limited self control. The more exciting the dog, the less brains my dog has when I take off her leash.
We've done a lot a lot of work, but it's all in an agility setting. I'll send her through the weaves and have someone run the opposite direction past her. I'll run her down a straight line of 4-5 jumps while someone runs parallel to me (or even harder, the opposite direction) with their dog. My trainer will send her crazy dog through the tunnel or over the a-frame while I'll demand focus from Lucy and stuff her with cheese.
We're making progress, but it's SLOW. It's a million times better than it was when we started 4 years ago, but it's a battle I think I'm going to fight her entire life.
Good work with Didgie!