Paul Morrissette mentions geotextile. One can get what is probably the
 equivalent from garden supply places called landscape fabric. The material
 allows passage of moisture but not roots (much) and would be clearly better
 than sealing in/out the moisture from a feature which had reach equilibrium.
 
If one is interested in removing a feature intact for later display, you can
 impregnate it with the equivalent of airplane glue. I have used styrofoam meat
 trays (new or used, depending upon circumstance) dissolved in acetone or other
 organic solvents. Back in the lab, additional acetone is used to soften the
 soil block. I have not done this for several years and would now recommend
 finding a safer solvent to use, given cancer, liver damage, and flash explosion
 risks of many organic solvents.
 
The above can be used to preserve stratigraphic profiles as well. Another
 technique is using latex peals. This method preserves a record of the surface
 only, but for profiles or feature surfaces can be very useful. Paint the
 surface with latex, adding several coats, then while wet add cheesecloth for
 backing and another layer. It takes some experimenting, but is worthwhile when
 the situation is correct.
 
William H. Adams
P.O. Box 1177
Philomath, OR 97370-1177  USA
503-929-3102       -3264 fax
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