I would definitely shy away from doing the whole pen in pea gravel. The choice is yours of course. I would only use the pea gravel around your water sources. Its great for that. In the long term sand is better. I have been to several zoos and lots of avairies and everyone stays away from too much concrete or pea gravel due to the foot problems (bumblefoot in particular) caused by them in the long run. Dont want to debate this prior to others comments. Pointless cause I definitely wont budge on this one and they probably wont either. Again your choice.
