I have been thinking to end a raised piece of decking to build a long box ,fill it with soil ,place some chicken wire over it and then the last 20 mil with stones etc ,then plant semps...It will have a slope 45 degrees...

I am hoping that the semp`s will hook onto the chicken wire and if it rains hard they will stay put....

Is this a insane idea?

Nope, and hopefully the semps will hang onto the soil when they develop roots into the soil. Also use chx wire that has bigger holes to facilitate easier planting of root balls if any. In fact, here's some info that hopefully may help with your project:
http://garden.org/ideas/view/w...

Sounds like a great idea Mick! And it should have excellent drainage too.

webesemps said:
http://garden.org/ideas/view/w...

ahhhhhhhhhhhh now my garden will be full of pictures....love them...

Mick, I just know you will have tons of fun as your project is a much bigger and probably will be when done,
a showy one!!