This thread brings back some memories. My brother used to live right by the Elk River in Maryland, and we could walk up and down the bank and find arrowheads, especially after big storms. Farms are also great places, especially right after the fields are plowed, and some farmers didn't mind giving permission for people to go look for them. My dad found the most perfect arrowhead I've ever seen behind my brother's house. It looks just perfect, with notches on the side of base, just like the emblem on a boy scout's uniform! And not a chip on it, which is rare, especially on a big flint one like that. A lot of the ones we found were "bird points," smaller, triangular arrowheads, not much more than an inch on a side. We actually found a few of those that were made of quartz. I can't think of any way you could safely "mine" for them. They're mostly made of flint, and are quite delicate. A lot of the ones we found were broken already, at least at the tip. It's a real treasure to find a complete one. Even just digging for them, you're likely to put a shovel right through one before you know it.

You said your land borders a river? Like Coombro said, "the rains will bring them out." Check the sandy or pebbly banks, especially right after a good storm has stirred things up. That's how we found a lot of them back in MD. Good luck!