Okay, it won't get you a silver dollar, but here are a couple of sites that have higher than average potential for half dollars.
• Pre-1964 parking areas near county and state fairs. These weren't paved, and often the grass was still at least ankle-high even after mowing. The parking fee back in, say, the 40's and 50's, was usually 50¢ or $1. Remember, these were very large areas— they had to be— and even if they've been hunted many times, you can bet the other guys missed at least a few. In some cases, they were on private property adjoining the fairgrounds; so, in places like that, there's a chance they've never been hunted at all. Trust me... I'm not guessing about this one!
• Vacant lots where Christmas trees were sold back when silver was still in circulation. Many of these were fairly grassy, too, and of course some were also covered with snow at the time, making it even easier to lose coins. Locally cut trees were generally only a buck or two, so a lot of quarters and half dollars changed hands. I can remember when this was a popular moneymaker for Scout troops, 4H, FFA, and school classes. Older folks can probably tell you where some of these lots were located in or near your town.