Teclis is normally guarded by Caradryan. And camped in a big unit.
Besides, the whole point of why Teclis is hard to kill is because he sends out more successful spells than an Oxbridge spelling comp.
Anyone who's anyone won't let your Gauntlet of the Duel near him without either spell blasting you, or have Teclis exit out of the back of the unit.
At which point, Caradryan accepts/issues a challenge and slays your Lord.