Crossing Central American borders with dogs?

[KootenayRambler]

I am planning an expedition into the heart of Central America. I'd like to hitch from British Columbia to Costa Rica and back. Im wondering if anyones had any experience crossing over borders, on foot, with their dog? I understand the certification needed for the US border, but I hear it can be a little hazy the further you go South. Also, i'd be glad to hear from anyone else who's done a similar trip with their pooch. I've met folks who've taken their furry nomads into Mexico, but never any farther down than that.