My wife and I scrapped our fire pit design because we got tired of pulling weeds from the surrounding pond rocks every year, even despite putting down plastic between the dirt and pond rocks. We bought paver stones from Lowe's to make our fire pit surround, then put the fire pit we already had inside of it, and filled in the space with the pond rocks that used to be on the outside of the fire pit. I know this is probably a really dumb question, but is there any danger to having the fire pit so close to the pond rocks, once it gets really hot from having logs/coals in it? There's still a little bit of work we have to do, but the picture below is the general idea.
You'll be fine. The rocks will be hot due to the proximity of the fire pit, but the fire pit will also be hot enough that you really wouldn't be touching that area anyways. I would suggest not dousing the fire with water until its cooled down considerably though. Once the rocks get hot, pouring water on them will cause them to crack and spawl.