Why we did not use magnets.
Magnetic tee retention sounds clever. Here is why it does not survive a real strike.
The magnetic-tee category
Several products try to retain a tee with a magnet embedded in a base plate. The pitch: the tee snaps back to the magnet after a strike. Reality: a driver swing puts roughly 100mph of velocity into the tee. No practical neodymium magnet thin enough to fit in a mat retains the tee at that speed.
The synthetic-grass problem
Even if you solve the holding force, the magnetic field has to act through the synthetic grass layer. Distance kills magnetic force by the cube. By the time the field reaches the tee, it is too weak to matter.
The clutter problem
Magnets attract ferrous junk. A magnetic mat plate collects metal shavings from cleats, ball markers, and the small ferrous bits that accumulate in any hitting bay. Within a month it is filthy.
Why cord wins
A 1.5mm cord acts at full strength regardless of swing speed, mat thickness, or environmental clutter. Mechanical retention beats magnetic retention for this use case.