This is such a difficult problem, one method I have used in the past is by cutting lengths of cane and pushing them into the trough/ planters leaving them about six inches high, this I have done in flower beds too, with flower beds and borders I think the secret is to try and plant them up so that no earth can be seen, I have used carpet roses with good affect, I can sympathise with your neighbour as this can be so frustrating.

Oh yes it's such a pain. Years ago I bought some 6x fertiliser and i noticed that my then cat constantly avoided it. I haven't had another cat since then so I'm afraid I can't attest to the aversion being replicated. 6x is very smelly fertiliser and widely available I think.

Having your own cat is the best one(not something everybody can or wishes to do!) but put cat repellent into Google and there are several said to be effective. In the meantime try sprinkling pepper on the plants. Once the smell is there it takes a lot of getting rid of. Silent Roar might work (its dried lion poo)

Cats don't like strong odors so anything with a strong smell would deter cats - garlic, citrus, mint, pine, hot sauce. Cats won't go anywhere near my sage plant so I'm using that too. Sage is a really nice addition to any garden regardless with its silvery leaves and blue flowers - a delicious herb and very ornamental and now - deters cats too.

Rue (Ruta graveolens) has been an effective cat repellent for me. They also don't much like big, pointy pebbles on the soil.

Thank you everyone for all these helpful replies and ideas. I have made a list to take round to my friend.

I found a drop of Jeyes Fluid,or Olbas oil,sprinkled sparingly on used tea bags,and left on the areas used by cats,worked well for me.Need to keep replenishing,as the smell of the deterrent fades.I've also used rose cuttings,used in a criss cross way,so there are no spaces to get between,but it's quite unsightly to look at....good luck,with whatever your friend decides to try..

Thanks bloomer, That sounds like another good idea. I think my friend will be trying out all these ideas, so desperate is she to save her precious plants.

Vacuum cleaner fluff deters deer & squirrels, maybe it will work for cats too - It's worth a try. Its free fertilizer anyway. Just empty the vaccuum cleaner into the flower bed.

Worth a try, bathgate. Unlike me my friend is is a vacuum cleaner enthusiast so I will pass the message on!