Wow thanks to all for the great response. There is a lot of good information here.
The cache was a 1/1.5 (I took 4 of my five kids on this one, ages 4 - 11). The datum and units are correct on my GPS. There were several suggestions involving antennas. As an engineer and an ametuer radio operator I can understand the need for something better than the little patch antenna in my etrex legend and I may try to find something practicle to help with Late spring and summer caching, but It sounds like there are serveral things that we can try without having to add to my techie stock pile.
Thot brought up a point that I've been thinking about all week. The cache listing said that the cache was "about" 100 feet off the trail. On the trail we never got closer than 193 feet. We did go bushwacking and got closer readings but never spotted anything that jived with any of the other clues. When I do the math, that puts my GPS off by almost 100 feet. At the time, that seemed more than an about would account for, but maybe I just don't have enough experience with geospeek yet. We didn't check to see how many sattalites were locked or what the tolerance was on the distance while we were on the trail. That's something that I'll remember to check from now on.
If I can trust the bearing and distance readings no matter how fast I'm moving (assuming I've locked enough sattalites). Then using a magnetic compass to get a heading, and the GPS for distance sounds like a good idea to try as well. I have cerebral paulsy which in my case isn't really too bad considering some of the cases I've seen. I can walk without crutches or braces and as long as the terrain doesn't require any balancing act or slopes that allow gravity to pull harder than I can compensate for with my own legs (ie I can walk up or down the hill) then I'm willing to try almost anything. I have to go real slow sometimes if there are obstacles to step over or around. The compass on the legend is almost worthless when I've got to slow down so I need some sort of replacement, either a magnetic compass or a GPS with a compass that doesn't care how fast I'm moving.
BTW the cache we were after was GCDDD1 if anyone is interested in Missouri caches, the park this is in (St. Francois State Park) is really nice for hiking and hence caching as well. There are a total of five that are on our list to conquer and I think most of them are easy enough for the whole family, at least based on the d/t scores.