Thanks! How about the Tranny?
The most effective method is to just take it to a shop every 30,000 miles and have it flushed with a machine. This generally does not include replacement of the filter, but that is not a huge issue.
The thing about transmission filters is that transmissions are a closed system. The only "dirt" (the particulate matter from the clutches wearing as they engage) they produce either deposits on the magnet in the pan or stays suspended in the fluid because it is generally too fine to be caught by the filter. By the time a transmission filter has enough junk in it to actually need replacing, you need a new transmission because those are pieces of gear and case and what not.
In fact, a lot of newer transmission designs, like the series in the Edge, Escape, Explorer, Flex, and Taurus don't even have a filter anymore. Just a screen bolted in between the valve body and solenoid pack.