It could be the dog but I think the membrane and bark mulch is keeping the roots damp and Choisya prefer free draining soil. They are from dry Arizona/Texas/Mexico region so are used to dry conditions, not humid and damp. I would remove as much membrane as possible. The bark should provide enough weed control by itself.

I agree with kildermorie I have 6 and all are free draining soil all I do is mulch around the base once a year, we have a pack of feral cats here which pee/poo all near them and they are still going strong so it's probably not that.

Just out of interest (if anybody is interested) the wee of boy dogs in small quantities doesn't usually cause flora to have problems. Girl dogs (but not cats) are a different thing. A drop of their wee can kill a plant. I speak from experience and professional knowledge.

I'd like to know where in the country these Choisya have been planted, and whether they're Sundance or the plain green variety - in colder parts, they prefer the shelter of a wall and don't do well exposed to cold winds. As the UK generally gets much more wind than it used to five years, ago, and these are planted along a drive, is it possible they're too exposed? And if they're the Sundance variety, these are even more susceptible to cold winter winds.

I agree with Bamboo. The Golden choisya "Sundance" in particular isn't fully hardy. I've also see the green variety damaged by exposure to hard frosts in exposed positions

@Anchorman.

I find plants will be much less damaged by frost if the soil is dry. Wet, damp and freezing is deadly for semi-hardy plants like Choisya. I stand by my comment of removing the membrane.

thanks everyone for your help the drive is very exposed and due to the weather we have had the ground is wet and the membrane will have to go.also there right next to the river severn so we get lots of wind.I think they are the plain green ones will get the name and post later.Our location is berkeley gloucestershire. We have given them a feed and so compost to see if that will help.thanks again rockford

You can cut them all back and remove all damaged growth and reshape when the weather warms up, say around early May. This will induce new, healthy growth, although, given their exposed situation, more damage will probably occur next winter. If they're plain green, they'll be Choisya ternata - just so long as they're not the variety C. ternata 'Aztec Pearl', the leaves of which are a lot more delicate.

hi they are the choisya ternata we have started to remove the membrane will tell them to remove damaged growth.4 of them are almost all damage do you think we should try cutting these back or just have them out.Its so sad to see because they all looked so well and were growing big.they have spent so much money on these plants the nursery guy came and put them in you would have thought he'd know the wind would be to much for them.Well lets hope with you guys help we can save some of them. thanks again have a good weekend rockford

Try cutting back the really bad ones to see if there's any sign of life inside the stems. If so they'll recover quickly but may die back again next winter