From: April 19th's of http://www.worldwidewords.org/maillist/index.htm
Hodmandod Several readers forwarded a reference in Alfred Watkins’ book of 1925, The Old Straight Track, about the ancient tracks or ley lines that he believed criss-cross the British Isles. Richard Mellish wrote, “He had a theory that the original dodman was a surveyor carrying two poles, used to establish a sightline from one hilltop to another. The snail, with its ‘horns’, would thus have been named after the man with his poles. Your information about the word dod for a hilltop would support the theory.” However, Watkins derived the word from the Welsh dodi, to lay or place, and from dodge, associating it with the actions of a surveyor moving his surveying rod back and forth until it accurately lined up with another one.