You're best bet is to buy a front hitch and install one of those hitch D-Rings or buy a base plate set for a tow bar.
To me the base plate seems to make more sense, as I don't think you'd have to specifically buy a hitch D-Ring, I'm pretty sure you could just use normal D-Rings (not sure - no personal experience in the matter). Check out etrailer.com for either way.
You can also apparently get a tow hook from the dealer that came on internationally shipped Explorers, but this tow hook is way under your truck and quite inaccessible for a lot of stuck scenarios I can think of (it mounts on the front IFS support just behind the plastic radiator shield).
