Old Wall & Fence? at Deerbolt, Grasmere

Yesterday whilst walking from Grasmere, via Rydal to Ambleside, went through Deerbolt Woods, and then at the gate at the top which brings you to Loughrigg Terrace, the random wall had stones with circular cut-outs above one another to enable fence post to be put in through the holes which would then extend the wall even higher with fixed net wire. This wall looked very old, just like the method of fixing post.

I could not help but think, but why? If you were putting these in whilst building the wall, why would you not build the wall a little higher in the first place! I wonder if it was to preserve stone? (Click over photos to enlarge)