I recently installed some flat neodymium magnets between the rails, and they seem to work as well, or better, than the round ones being talked about. These are 3/8 x 1/4 x 1/32, magnetized across the length. I just ACC two of them, on the ties, spacing one next to the one rail, and the other one at the opposite rail. This spacing puts the trip lever of the coupler right over the appropriate magnet. These are available from Edmund Scientifics, part #3082273, bag of 16 for 4.95. Try 'em, you might like 'em.
I will pole-litely go to their sight as attracted to it as I am, I certainly won’t go south on those, I’ll go get linked up with them.
Those bigger ones are so strong you can actually put them under the ties. Cut a hole in the road bed and lay the track over them. Just practice on a test strip so get the positioning correct.