not to be a buzz kill BUT, if all you're gonna dig is 70 and up whats the purpose of detecting.
dont you want to find the good stuff. i dug a 1917 walker half yesterday, its worth only about 20-30 dollars.. I want to find the gold rings and jewlery. knocking out nickles and zinc means you're hunting mostly coins. you can buy all the coins you want on ebay for what that AT pro cost you.Indian heads on ebay 50 for $30 those are from the 1800s
you will get tired of clad...open it up find the good stuff and make this hobby last.
i get frustrated sometimes and do just this even as high up as 80. but i soon realize i aint here for clad. silver coins are not that plentiful so jewelry is really what i'm after and old silver of course.
just as a data point i found the walker with the etrac. i mostly use the AT pro in the lake...zero disc.