These used to be available for sale on sites like Hammacher until they were panned for how bad they were
You can incorporate detectors into anything into which you can isolate a transmitting and receiving coil connected to circuitry/software to manage the electromagnetic signals and look for variations to alert on. You would need a sophisticated technology to ground balance the detector on the fly since it’s pointed into the soil and you have a constant variations of height in a shoe (walking.) Even with today’s best units, the performance of a “shoe metal detector” would be horrible. The signals would be lost in the noise and depth would be pathetic.
Coverage is another reason not to do this. A regular detector is like coloring a sheet of paper with a wide marker, where this would be like using a very sharp pencil. Our footsteps only cover a tiny percentage of coverage (100 square centimeters, therefore 200 square centimeters for 2 feet) versus around 3x this for a basic detecting coil. Then, add in the swing, and you have more than 50x the coverage of the bottom of a foot (unless you plan to swing your foot back and forth, which would get exhausting – and only cover 1/5th the area of a normal detector’s swing!) [this was back of the napkin calculation, I welcome improvements on my results]
If the reasoning here is to be covert, I would ask why? Prohibited areas are prohibited for a reason, often because they are Archaeological sites and here, nighthawks, trespassers and looters are the scourge of the hobby detecting community.
Why would you go to so much trouble to create a poorly functioning solution like this unless you had a plan to be secretive? If you do, I hope you are arrested and forced to watch as the prosecution holds up your ridiculous metal detecting sandals as evidence in a court of law. Please someone send me a picture if this happens.
Not to assume this, I can see other reasons for this, such as landmine detection, but honestly you may not know you have a mine until you step on it.
Bad idea, just get a lightweight detector.