Cat sprays on neighbor balcony

My cat, a fixed male, loves to visit around the neighborhood. One of
my neighbors "Anne" said that she likes to have my cat visit, because
he is company for her (indoor) cat. He used to snuggle on her bed
with her cat, but she doesn't let him in the house anymore because he
SPRAYS. Now on her balcony,and it smellsl. He NEVER did this at home!

I remember we went through this some years ago, and I suggested she
spray him with water to discourage him. But she doesn't want to do
that! I'm not sure where she's coming from; she is not at all
hostile; says her cat loves the company. I said I would research if
there is anything she can apply to her balcony to wipe out the traces
of the smell, so he won't do it any more.

Help!