Counterflow chillers

I've built one of these previously and had all sorts of issues with it and gone to immersion which is pretty good.  The CFC I built was 15 of copper pipe tightly wrapped and inserted into a large dia. plastic pipe with both ends capped.  Each cap had a hose connection for cold in and hot out as well as terminal fittings on the copper.  Blocked every time and leaked like an old dear.

Anyway, I am part way through building a hop back to filter my hot wort and add some nice hop finish.  The hop back is being used to filter and the wort will be hot, but unfortunately the chiller unit is in the boil kettle.  I could move it to the fermenter but not sure about the hot liquid in plastic, also there is a much greater chance of scratching my fermenters with the copper chiller.

An option I was looking at was a gravity feed from the boil kettle, to the hop back and through the chiller to the fermenter.  Using either a counterflow or plate chiller.

Anyone using these well and can give me some pointers on how you stop them from blocking with hop or trub matter?  What sort of maintenance to keep them clean etc.?  Same with a plate chiller?

http://www.homebrewtalk.com/f51/counterflow-wort-chiller-build-use-...

Something like this

The primary option is for me to use the immersion chiller in the boil kettle as normal and run the pump to circulate the wort through the hop back and return it to the boil kettle.  I think this will work ok but I'm a little nervous that the hop back might block once the trub and hop pellet matter starts to fill up the hop back as its filtered out.  I might use a 1" outlet to compensate.  Getting a couple of screen cut for it tomorrow which should help.

Worth a bash anyway :)