3. Collection grid - Spacing should be 2 m for a border collie sized dog. Smaller dogs you could go 1.5 to 1.75. Height of bars for Keen was 200 for the first 3 and 300 for the last one. 
In this exercise we are wanting them to add an extra stride in before the last jump when we are standing about halfway between the last two jumps in decel. Use a clicker if you have one to mark that second stride. You can play around with where you place the reward in that gap to help them add it. If you are using food I would use a container with a lid or make sure you can beat your dog to the food if it's not covered. 
When they are at the point of adding that stride do one or two reps out in front of the grid to show them what extension looks like. For that they shouldn't add any strides in the gaps. 
Then go back to see if they can do the collection stride again. Once they are doing the collection stride well you can have the reward on you to see if they can still add that stride. 
The next step from that would be to add some motion from you but make sure you get to decel when they are between 2 and 3 and they should still add that stride.