leg layering

I don't have any recommendations on rain pants, but the long johns will tear easily from abuse because they are made to be worn under pants. You should look into running tights, much more durable. Not durable enough for serious bushwacking but enough for rocks and the occasional bush or sharp branch. I like the golite running tights.

I like GoLite's Goretex Paclite rain pants. They've been very durable.

The other option is to get something cheap, like the Sierra Designs Microlight pants, and then not worry about durability.

The next time you're at Goodwill, look for unlined running "warm up" nylon pants. They typically weigh 6oz and can be dirt cheap, making it less painful if they get shredded. Many have good DWR too; I've worn them during morning hiking on trails overgrown with brush and heavy dew which can really soak you.

Rain pants that will take some abuse are also fairly heavy. 3 layer pants are about 10-12oz at best.