It is always one of the most important parts of keeping swine, the first thing you do when you get them or 1 is to confine them to a very small area where you want them to deficate, away from a water source. once they have soiled the area several times and this may only take a couple of hours, then you can open the pen back up to them. They also like to crap & pee near water so it's important to seperate these, they will now go in one place and one place only, pig's are very clean in that regard contrary to popular belief.
Now as far as your pig is concerned your too late once he set his toilette it will always be his spot, so your out of luck and I hope others will not try to sway you to try some goofy ole wifes tale about how to rid him of the spot, can't happen IMO, unless you re-pen him using the method above and keep him from ever going back to that old pen.
AL