Which ones specifically?

If you want to use radio, the most practical approach is using RSSI (Received Signal Strength Indication). You'll have to calibrate it, but basically it means not using ToF but using relative signal strength.

Alternatively, you could use the method employed by the "invisible" dog fences and bury a perimeter wire that provides a weak signal only receivable in close proximity to it. While burying the wire might seem burdensome using the slanted cut method with a wire burial shovel is actually quick and easy.

You might also consider ToF but using "smart" markers. That is, have the markers check how far away the vehicle with radar or laser range finding (cheap modules) and report to the vehicle. This has the advantage of simplicity because the vehicle will be much easier to identify than the marker.

You could use RSSI in the smart marker as well, listening for the approach of the vehicles beacon. UWB would work very well for that, it would even work well with simple UWB beacons and the intelligence on-board the vehicle.

You might want to investigate this last idea first, since it has the potential for being the most accurate and least prone to having the markers be obscured (if using light). It will not be the cheapest solution, but isn't prohibitively expensive either. Ultra Wide Band is impressive stuff. (Think AirTags, etc.) Modules are available at a reasonable price.

 

re the max35101
it has good resolution, 20 ps, but it has a 8 us minimum time of flight