I don’t know that much about outdoor model railroads but inside some folks run feeder wires every three feet or so but that sounds impractical to me for your issue.

A neat product you may want to consider is something called Wire Glue from Anders Products. It looks like black toothpaste and you can use it as a solder substitute. Just apply some at each rail joint and allow it to dry over night. It will become quite hard so be sure that you don’t make any lumps of the product during its application that could derail your trains.

Here is the web site is where you can buy some:

http://www.andersproducts.com

Hope this helps,

Geof from the US