The best way to wight hunt is to get a ghol in the enemies back field and run them down. However this strat is quickly being countered by center plugs on desert and creep. Having the ghols go all the way around N or S and therefore not being able to catch wights heading for the water.  Also archers make excellent wight guards because they can shoot down ghols before they can even get close to the wight. The next way is with a thrall. However people now include thrall guards with their wights. So if you really want to get those wights out of there meet his thrall guards under water with a larger thrall attack force. Once the enemy thrall are dead you can chase the wight. However the wight is still faster then the thrall and can get out of trouble. This is where more ghols in the back field can come in handy as they can run up and hopefully pop the wights before they recieve any  extra guards. If you don't want to try this just have your thrall stay in the water and chase the wight out again if it tries to get back in. You can also conduct thrall sweeps up a body of water in search of wights. Just walk your thrall normally up the river if you suspect wights are nearby. Have them stop at certain intervals. If any wights are present the AI will react and chase them out. In FFA's you won't be so aware of or concerned about a wight's presence as in a 2 player game. This is many a players downfall on Carnage. You can hear wights even when you can't see them (either underwater or out of your range of vision) so at the begginning of FFA's and large two team games I like to check starting points for the tell tale sound wights make which is buzzing flies.