The steps to a good 2-on 2-off (stopped) contact behaviour

1.  Hind end awareness
2. Hind end targeting
3. Rewarding in situ
4. Back chaining
5. Proofing

​1. Hind end awareness

There are several exercises for teaching hind end awareness. With contact behaviour in mind, teaching walking backwards is a useful first step. This can be taught using shaping. Reward for taking one step backwards. If this doesn’t happen lean into your dog and then reward for a backward step. Once they are reliably taking one step back increase the expectation to two steps and so on.
> How to train your dog to walk backwards - Success dogs website
> Teaching hind end awareness - 2-on-2-off agility foundation - AKC website 

2. ​Hind end targeting

Once the dog has mastered walking backwards, place a board on the ground behind him and ask him  to walk backwards. When one foot is on the board reward. Increase the requirement to two hind legs. Give massive reward for remaining in position. Hold off the reward for a few seconds to lengthen the time the dog is on the target, then release.
Once the dog is consistent at finding the target and remaining on it until released, increase the distractions, such as handler movement, a toy on the ground etc.

3. ​Rewarding on a ramp

Move the plank to the bottom of a sloping ramp, step or the bottom of a dogwalk/crossover. Reward backing up on to the ramp. Remove the plank as soon as the dog backs onto it consistently. ​

4. ​Proofing

Proof the 2 on 2 off position. With the dog in position, move away slowly and reward. Then start introducing more movement, running, jumping. Introduce static and then moving toys. Tug with the dog in position, stop tugging as soon as one hind foot comes off the ramp. Wait for the dog to get back into position and restart tugging.

5. Running into position

Place the dog a few steps above the contact position. Reward stopping in the 2o2o position. Gradually place the dog higher on the ramp, rewarding fast accurate 2020 behaviour. Increase the distance until the dog is confidently running along the whole ramp. Proof each change of distance.
> Contact training - One Mind Dogs website
> Agility obstacle training dog walk - One Mind Dogs website