I think around 10-12% or so would be appropriate for gate (i.e. wasting 1-1.5 squares over ideal buildings but it's worth an awful lot of event dailies at that point to get 3+ level 2 sentinel outposts). Given the limited options for defense boost, I'd probably place some then and hope to replace at some point. 4% is not worth placing except for the very beginning of a city when you're using it for the happy and the defense is just a bonus.
3% for the face seems fine (3% is good enough as a freebie - i'll place some in most of my cities as I get them but hope to replace them eventually, 4% would be normal for a 2x2 with no road, 5% would be chase-tier if you're trying to stack attack)
3% for the face seems fine (3% is good enough as a freebie - i'll place some in most of my cities as I get them but hope to replace them eventually, 4% would be normal for a 2x2 with no road, 5% would be chase-tier if you're trying to stack attack)