When using an Adjacent Slide defense the goal is to lock off the crease, denying the ball to the man in front of the goal. This is a great defense to run against a team who has a strong crease man, but also means your defense is not sliding from the crease.
It is generally a bad idea to do this when there are two men on the crease because the adjacent slide would be much longer and the second defender on the crease, as second slide, should have a good chance of covering for the first slide.
On the other hand if there is nobody in the crease the adjacent slide is the only option.
Ideally you want to force the midfielders down the alley when executing this slide package. The key is to reinforce to your players that if they get beat they must get beat to the outside, not down the middle, and the general terminology is for the defenders to "Stay Topside". Sweeps and inside rolls are very dangerous against this defense, not perhaps for the first slide since the first side is in relatively good position to stop a sweep to the center, but more for the domino effect of openings the center drive creates for the offense if they can complete one or two passes.