Complex Navigation

I making an rts game where the units don’t have a collision with each other and they are walking to a grid space areas, but at the same time there can be only one unit standing still at a location of choice or as I call it grid position.
When I was using xna I had more control with the pathfinder of A*, I could do formation I could do roads but here I don’t have a clue what can I do at all, and can’t find anything.

Short version:
1.Need to know how to have an navmesh (or magic) areas where units can’t stop but can walk on.
2.Need to know how to have more complex navigation control if possible at all.
3.Thanks for any help.

Lots of years passed since I asked this question now that I abounded my RTS project I will never need the answer but here it is anyway.
1.Nav MoModifier I was looking for that.
2.Here I would just add more logic before the navigation itself, in my case I wanted the units to go in grids so here I would just create a Map that will show them where they can go and where they can stay, of course I would set their locationToGoTo = locationToGoTo / GridSize so they would really move into grids.
3.Your welcome.