Let’s talk about spies. When, which, how?

What’s your preferred spy strat? Of course it’s dependent on opponent, but in general what’s your favorite?

Do you dump tens of spies on one prov? Do you keep them there even if some get caught? What’s your mix of economical to military? Do you spread on which resource?

I’ve been rotating strata lately which might be the best strat. Each has downsides. My spread right now is 2 military and 4 economical on 4-5 provs of a country of the same resource then I rotate that resource every day. But I might switch it up and dump all on one for a day.