I use weighted plastic 4" dia.drain pipe capped on one end. Inside I add some filter batting for them to nestle into. Remember they require an open hole in the event of long term winter ice just as fish do for gas exchange.

That sounds like a good idea frogman. How long is the pipe and why cap one end? Anyone else have something that has worked?

I use 6-8 inch long pipe. I would imagine only one frog would use each pipe. I plug one end to lessen the chance of them being disturbed by fish. That's what they are looking for a secure area to sleep the winter away. It seems to be real hard on them if they experience a warm snap in late winter which brings them out of their slumber only to have the temperatures drop back to normal. The weak ones do not usually survive in my experience.

We have only one green frog-- will he find the pipe or should I use several? And can you please tell me what filter batting is and where I might find it? I have a feeling that, since we've had some cold nights, he may be already hibernating. There is a terracotta pipe, open ended, in the deep end of the pond (for the fish to "hide" in if there is a predator),and I wonder if the frog could be in there...

Most frogs bury themselves in loose soil to hibernate.

I put two frog caves in the pond this week for the first time. I used a flat rock about 1 foot square and 1 inch thick, held up by three rectangular stones about 3-4" high. I put layers of quilt batting in the void under the flat rocks to give a soft secure place for a frog to sleep. They are located away from my fish hole that has two large fish caves. That is so the fish wont try to use them and disturb a frog. I have 3 large green frogs and 1 medium one. It would nice if they all servive the winter this year. I hope its not to late in the year and that they can still find them. We had a cold snap last night :-(
Mike