Hey southwest,
I don't know how safe any of them are for use around the pond. I refinished mine last summer and used Cabots Australian timber oil. After reading up on the stuff it sounded like it would be good since my deck was also old and dry. The stuff supposedly soaks in to the wood and after using it, I would agree. The finish wasn't quite as nice as I had hoped for but it did make a huge difference.

When applying it, I used a brush and was very careful to try and avoid any excess to keep from dripping any into the water. Time consuming but better than taking a risk of spraying it in the water. I'm sure any product you use would be fine with careful application.

I'm going to go out on a limb and guess that any minimal amount that gets in the pond would probably be diluted to the point of not being harmful. If you were to accidentally drop the entire gallon in then I would say there would be consequences. Sorry I can't help ya more but that's how I did mine.