[Verjigorm]

We can examine the cost of various counters:

Assumption: 6 gems = 100gp
Abomination Cost: 25 pearls (Level 9 Conj)
Dome of Arcane Warding: 10+ (Level 6 Ench)
Watchtower: 200gp (12 "gems") (Equiv. Level 0 Spell)
Ghost Riders: 5 gems (Level 9 Conj)

First, the Abomination:

Abominations have 4 attacks: 3 Life Drain attacks and 1 Gaze of Death. All of these effects are, generally, useless against a Wraith Lord, so it comes down to basic statistics--the Abomination is simply a better unit. It regenerates 27hp per round as well... Unfortunately, the Wraith Lord gets a Bane Blade, so he still has a chance to kill your precious, exensive Abomination. We'll take Bummer's assumption that an Abom can deter 1.5 GR spells... 1.5 X GR = 10 1 x Abom = 25.

Abomination is not cost effective

Dome of Arcane Warding: 10 + duration
DOAW blocks 50% of all GR spells. If a GR spell gets through the dome, and the province is not well-defended, the dome is destroyed and the gems wasted. Assuming 1 cast per round, the dome will probably be useful only 1 time (assumption: the dome works the first time and fails the second). 10 gems for 1 block costs opponent an extra 5 gems. DOAW is (very shakily) equivalent in cost to GR.

Watchtower: equivalent of 12 gems, blocks all GR castings.
Clearly this method is quite effective.

Some others:

Dome of Solid Air: Breaks when penetrated, 80% protection, cost 20 gems. This one is much more effective against GR, but it can be brought down (usually by a barrage of cheap spells e.g. Seeking Arrow).

Mechanical Militia: 5 mechanical men adds significant power to PD, but is it enough to combat GR? I haven't tested it. This spell however is expensive and dispellable.

Haunted Forest/Enchanted Forest: HF with death scale can provide some Manikin, Enchanted Forest with growth provides an increasing number of Vinemen (neither of which will run from the WL). Can they handle GR? I'm thinking HF = no, EF = no (unless you have an ungodly amount of them). Of course both spells are very costly and can be dispelled and possibly defeated by the GR.

Wizard's Tower (the spell) costs 50 gems, a lot more than a simple watchtower (or even Castles, Hill Forts etc.)

Three red Seconds costs 120 blood slaves. Blood nations can often achieve a sufficient hunting rate to make 1 a round, but a standard fortress is MUCH cheaper (you can't convert blood slaves to gold...unless you trade them to another player.)