Bajanick.......Not a totally silly idea, but a few things come quickly to my mind. (a) the rollers would need to be swivel ,or omnidirectional, so as to respond easily to any directional changes as you move the coil over the ground, (b) all materials used to make these rollers would need to be nonmetallic, so as not to drive the detector circuitry nuts, (c) weigh just a few ounces, since we are all looking for light weight detectors for less arm and shoulder fatigue and (d) you would need to discover a good way to fasten these rollers to the coil (no adhesives or epoxies with a metallic substance added for strength, such as the newer Titanium silicone caulks, as this would probably screw up the signals too. However, if you decided to affix the rollers with an adhesive, I'm pretty sure you could find an appropriate and strong product.....there are literally thousands to choose from, albeit, it would take some investigation.
If you are the inventor, entrepreneur type, with the time and
money to develop a new product, go for it and good luck !
Been there, done that, and can tell you it's a h--- of a lot easier to come up with an idea than it is to develop a good working prototype, sell the idea to a manufacturer and get it marketed.
Not trying to poo-poo your idea here, but it's like investing in the stock market, a gamble.
Hope this gives you something to think about in a positive way.
Todd