Bob,
I don't set anywhere near 250 decoys you do but I do set about 50. We use parachute cord about 3 ft long tied directly to the decoy and on the other end, long line clips (see this site for these)
http://www.atagulf.com/cgi-local/web...cgi?reset=4775. We then clip the decoys to the tarred line and use old sash weights for anchors. We have found that the 3 ft drop from the decoy to the long line allows the dogs to swim thru without a problem.
The tarred line is quite stiff and we don't get a lot of tangles. I've used spools from Home Depot that are used for long extension cords to store them.
Dave