I never did any collection work with Travis. When I would walk a course and decide how and when I would cue Travis for the various obstacles, I would have to consider where he would be landing and what the next obstacle looks like from that spot. Depending on his likely speed at that point in the course, I may have to plan for a landing that could be several feet farther than you might think.
Here are 2 pictures of Travis showing extension. The first one, Travis started the triple bar long before the jump. The takeoff spot would have been out of the frame of this picture. The second one, Travis is going to land some distance away from the jump.
For you folks out there that think agility looks fun, but people like me make it look so complicated. Please do not let me discourage you. It can be as complicated as you want to make it. I started out with Jes in 1999 (I think) and my goal was simply for her to learn how to do all of the obstacles. I didn't even plan to compete. Almost 10 years later, agility still gives me more to learn and new goals to achieve. I would love to inspire you to just build a couple of jumps and to have fun in your backyard or take an agility class. You can get a lot from a once a week class.
Here are some links to building cheap and easy jumps, slightly more professional looking jumps, and a website where you can order a kit to build your own agility obstacles.