Some LGDs have been known to have reactions to flea collars and pesticides. LGDs are outdoor dogs and flea collars will overload the pesicide if they get wet. On such a big dog, flea collars are not that useful anyway. Program and Advantage, as well as a regular spray regime of Dursban or Malathion have been known to be useful. A dog should not be allowed in the yard until you are absolutely sure that all pesticides are dry.
Most people recommend several days with no rain after spraying.
There are some LGD breeds which are even sensitive to heartworm medication. There are now biological alternatives to spraying the ground. Some of the newer flea control methods include Program and Advantage. Try adding goats milk, stewed boneless chicken and vegetables, other cooked meats to spice up the kibble. Realize that many of these dogs, especially working dogs or immature dogs will keep themselves lean.