Attention all former and current Drill Instructors

I need some help teaching drill movements to Young Marines. I have been working with our kids for 2 months now trying to teach them basic column movements, as well as obliques and flanks, and I need some pointers on how best to teach this. This past weekend I tried putting pieces of 100 mile an hour tape on the deck to show them where to pivot. It helped to some extent, but when drilling without the marks on the deck, they round off the corners constantly (no matter how much I yell :)) Obliques is a whole nother story. They definitely turn into a mob doing those! I really enjoy drill and teaching these kids how to do it, but I am starting to get frustrated and need some ideas. Maybe they need to do more pushups until they get it right. ha ha