Trying to decide which of the 2 options Lore mentioned depends on the stats (and covert level) of the person you are defending against.
Also increasing your covert level can help a ton if its feasible to do so.
If you play around with some of the calculators around you can get a better idea of how it works.
If you can add a little more spies (or if your online can train them remove them afterwords) to block the sab go that route. This will cause them to lose 50% of the men they sent I believe (or is it now all of them?)
You can also add in the lower/mid level weapons so instead of your big expensive ones they instead sab the lower level ones first basically wasting a 5% of the men sent on the sab to destroy those cheap weapons. Defense weapons are always sabbed first from smallest to largest. When they are gone it moves to strike weapons.
some examples using "prior" for the attacker ascension level:
10b covert on target
15B on attacker
lvl 20 covert 595,900 men required for the sab
If the covert level were 22 only 298,100 are needed.
This is why covert level plays huge factor in sabbing someone. If they are higher than you by 2 or more levels the amount needed are drastically reduced.
now back to the original 10b/15b/lvl 20 with realm alert set to critical on the sab would not work!
setting your alert level to crit boosts your "effective" covert skill by 70%.
(realm alerts increases you effective covert by 10%/20%/40%/70%)
They would need at least 17b covert and would require 1,013,000 men be sent at covert level 20.
with 17b covert and covert level 22 506,700 spies would be needed.
Remember crit also reduces your income by the same amount it boosts your covert but it does help against being sabbed and when coupled with nox can slow down how fast someone can attack you. More of an annoyance than anything else for someone that is determined
