I've been told by about a GPS that is a dream to use . It evidently attaches to the tractor by suction and keeps you on track according to figures you put in. Bad part- it sells for around a $1000. However ,with the high costs of chemicals , it wouldn't take long to pay for itself. I do have my homemade foam marker but on a boomless sprayer ,but the marker only gives a mark of where I have traveled and it is up to me to guess how far over to go. I have trails of weeds sometimes a foot wide or sometimes pie shaped where I have missed a bit . Then where I have overlapped , the pastures look good. Has anyone used these GPS units? I saw one on Messicks site but not sure if it is the same but would like first hand information or thoughts on this. Thanks , Bordercollie