So, just to qualify this suggestion before hand I think it's important to say this. I do not play an assassin and I have not applied for an assassin class token.
Background
Assassins have it pretty rough. Ever since the change happened where assassins now have to perform roleplay during the time of their attack, as opposed to before where they could roleplay then attack within 24 hours, the solo assassin has died out to people taking hit teams. Solo assassins however, a lot of people probably would affiliate it with the class fantasy of a delicate setup.
However, when a assassin roleplays to this person to build up the inevitable assassination attempt, the character in question can just lens in their face. Lenses are unstoppable unless you have someone in combat already, or there is existing teleport warding.
With this in mind, I suggest the following:
Assassins gain ESF Abjuration's Ward Teleport feature
The feature should however, not utalise the same VFX & animation as the original teleport ward, though if it came down to it that would be fine. I believe it should be an instant ability, 1 use/rest, and utalise a less intrusive VFX - maybe like the swirl effect from warlock's magic damage eldritch blast. The less intrustive VFX is simply to not scream to everyone in a potentially massive area precisely what just happened, even if they do get a notification in their combat log.
I also recommend this teleport block not be a big multi-hour one, but maybe only last 4 server ticks aka 20 minutes.
