How to maintain continuity with other surfaces when adding sculpt curves
The edges of networks without sculpt curves are always fixed. When you add sculpt curves, the edges of the network can be pushed or pulled out of position. This is undesirable if those edges need to maintain continuity with other surfaces.
To prevent network edges from moving, use the Pin Edge tool to “pin down” some edges down so they are not influenced by sculpt curves.
To show the curve network
toolbox, choose Surfaces > Curve Networks 
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Pin or unpin edges
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