[The Ghost of FReepers Past]

He can stop payment on a check, yes. But can he go to your bank after the check has cleared and take it back out of your account? That is what I am talking about.

[newgeezer]

But can he go to your bank after the check has cleared and take it back out of your account?

That's exactly what happens if he stops payment on a paper check after you've deposited it in your account. As long as he stops payment before it clears HIS account, you lose, just like the ACH process you're talking about. One is electronic; the other is paper.