Q: Isn't the Stack-Sack method of wall construction described in your March issue just a variation of the stream side-slope erosion prevention technique shown in the photograph?

A: One important difference, of course, is that the Stack-Sack technique is protected by patents, whereas, to the best of our knowledge, the use of sacked concrete for preventing erosion has never been patented. Just as a matter of interest, long after concrete had been used successfully for the construction of sidewalks, some bright lad applied for and obtained a patent on the idea, and for at least a while managed to collect royalties. The essence of the entrepreneurial spirit is often the recognition of the intrinsic possibilities of a concept rather than the creation of the concept itself.