the old Marx transformer, going around the tree for 47 years, was popping the circuit breaker after 2 or 3 minutes (transformer wasn't even warm) - so I found a new one for a really good deal on ebay.
the transformer deal is the 80-watt Lionel CW-80.
These retail for $130. But people are apparently parting them out from the Polar Express train set and selling them for $45.
Rock steady power for my little set.
Looks good! I have an HO set down in the basement that I bought from a friend for my four-year-old that I'd love to put around the tree, but I have to wait until he gets old enough not to smash his dinosaurs into it. (He loves watching Godzilla movies, and has asked for a Godzilla for Christmas. Wouldn't bode well for a train setup.)
I have the same problem with my Cat. I have a nice lionel christmas train that is great around the tree however my cat seems to think its her toy and knocks it off the tracks every chance she gets.