I use this plant-based cat repellent - it's a powder you scatter around the place and apparently they don't like the smell of it.
Can't say it works particularly well though - we have loads of cats around the place. I tend to just protect the plants as far as possible and I still have to scoop up the odd piece of, erm, 'contamination' in an inside-out carrier bag. 
Our nextdoor neighbours' cat is fairly well-behaved though, and is actually an expert mouse-catcher and bird-scarer, so we've not had many problems with peas/beans being snaffled! 
I do the whole thing of putting card, shredded personal documents etc in the compost - definitely makes a difference to the smell. It's about getting the balance right between 'browns' (paper, card etc) and 'greens' (vegetable waste) so the moisture levels are just right.
Apparently you can put shredded up cotton and wool clothing in compost heaps as well (the fabric is natural and therefore breaks down) - never tried this though...