possible invasion by cats- any cures

I have problems with either cats or birds constantly messing up the bark on my borders, this a new problem. This a new problem since I laid down a lair of fresh Bark.

 

Yes, disturbed soil or new soil, shingle or bark mulch can bring in the moggies.
There are lots of remedies out there, most you sprinkle on, and they work, but when it rains out you go again to replenish what's been washed away or lost it's potency due to water.
I've tried nearly all of them, and I have settled on a product called Pestban.
It is a gadget that works off the mains (battery ones are available) which sends out a high pitch sound that deters the cats.
I highly recommend them, as I have had some now for three years or more and have had no more cat droppings in the garden since.
Some people have said they don't work, but I speak from experience from the use of them and think they are great.