Buy a few replacement bricks, tear up a few over a big signal every few months, plus much easier targets just in the grass, rinse repeat. Don't view it as something you have to do in two days. Work that yard for years until the detector doesn't find anything anymore. Do it covertly on the sly with no single big interruptions or savages of your back yard.
If it was me (who is more selfish and really doesn't care what others think,) I'd take a vacation week from work, buy a gigantic normal size shovel, and just get it done quickly no matter who fusses at me. That's a hot lead that could gain you thousands of dollars, only a few steps away from your door, and only a foot or so down. No cops or others can interrupt you. It's hot-tip Candyland and Disneyworld, with free and easy delivery. How could a treasure-hunter not just vigorously go after this?