ZBrushCentral

How do I freeze or preserve edges while modelling shirt collars, pant opening and so

on?

I am making clothes and I would like the border shape of the collar border to remain unchangeable.

Use the Crease function on the Geometry palette to add an edge loop around the edge of your object. You can also choose to crease polygroup borders instead.

Crease is great while I am subdividing but it does not seem to protect the shape when sculpting. Would a polygroup make it impossible for any brush to alter the contour of the collar? Is a mask my only option?