Dont put ladders on decking, it doesnt get any simpler mate.
I in now way mean to be critiscising or nit-picking, but if you use a ladder on decking and the ladder slips (which it WILL, sooner rather than later most likely) and you fall off, paralysing yourself your insurance company wont wear it when you say
'Well, JSMC said it WOULD be okay to put some damp cloths down guv..........!'