Let's go back to first principles. I launch 3 mortor rounds at you. What would you need to do, to be able to detect, intercept and disable said rounds before

Let's go back to first principles. I launch 3 mortor rounds at you. What would you need to do, to be able to detect, intercept and disable said rounds before they reach you? I don't think anybody would say the cost to intercept and disable (whether by blowing up etc) those mortor rounds is even in the order of magnitude the cost of the 3 rounds and the mortor combined.