Try the tried and true suggestions from this website:
The 7 Deadly Homemade Weed Killers
BUT-for my money, you can buy a 2 1/2 gallon jug of 41% or 47% RoundUp or the generic equivalent for less money than the ingredients for homemade, with the exception of boiling water. However, if your drive is 700' long, boiling water might be difficult to pull off. A 2 1/2 gallon jug should last you a long time. Just don't leave the mixed solution in your sprayer or it will clog up pretty quickly. Always clean thoroughly when finished.
Most of the ag supply stores will have this. Stay away from the premixed products, unless you want to pay them for the water!
One thing about using glycophosphate products: Be sure to only use the recommended mix. Too little, and you won't get the results you are looking for. Too much, and you burn the top without killing the root. Be patient, as it may take 10-14 days to see results if the weather is cool.
If you've already been using RoundUp, you may have a lot of old weed seed still in the soil. Sad to say, but some of the weed seeds seem to have a half life like Uranium!!! Just have to keep after it.
Good luck, and welcome to TBN!
GGB