Wooden BBQ skewers, 100 in a pack for about a quid. You can use these to make things unpleasant to walk on and lie about on, This worked a treat where I had moggies nestling down onto some soft heather and using it as a toilet. Obviously use some sense to avoid where a cat would fall onto them and be genuinely injured rather than just poked. But you can effectively simulate some spikey stuff they'd rather avoid.
The lion poo (Silent Roar) is quite good, but you have to look after it - i.e. keep it dry and renew every now and again. Just a little bit is needed, perhaps tied in a plastic bag with some small holes in, or sheltered under the eaves of a shed etc.
I've found the green crystals and pepper powder less useful, but if there's going to be a warm spell you can scatter the pepper powder through shrubs etc which the cats rub through.
BTW, they dislike orange tango in their fur.
Oh yes, and putting the fear of YOU into them: Get a super soaker or large bucket of water. Be nice to the cats, get them really close. Then go postal on them. They avoid coming back.