Boar mate

[Plump82]

Gilbert and Freda are nearly a year old. We got them both neutered at 5 months. We've noticed that Gilbert often chases Freda, then grabs her by the neck from behind. She doesnt react at all. When he is chasing her other at other times she'll often turn round and chase him back, so the grabbing her neck isnt every time.
I had a look online and it seems this could be sexual aggression which can happen even if they are neutered.
While she doesn't seem to bother with it, it can't be nice surely? And despite being siblings he is almost double her size.
Ive came across a couple of websites that recommend boar mate or hog mate and it basically makes the female cat smell male.
Has anyone heard of this, or used it? I don't even know if its available in the uk.
Or does anyone have any suggestions on how we stop this behaviour?
Just for info, this only happens once or twice a week and we split them when we see it happening.

I read the title and wondered if this was a Guinea-Pig thread gone wandering into LitterTray ( I kept guinea-pigs for yeats . Our cats OTOH are a mystery to me)

The issue I can see with making your female cat smell male is your male cat spraying or fighting her rather than just jumping on her and annoying her .

We have a bro/sis neutered pair (2yo) .
He sometimes sniffs around her and I call "Eurgh that's your SISTER are you a Game of Thrones character , matey? "

Our female does a funny thing with her tail where she twists it over to one side . Not sure if its fertile season for cats now but I think some animals still think they are fertile ( Guinea Pigs most certainly do even castrated )

Can you get a water spray to give him a quick squoosh ?

Our pair did this occasionally. (Now 13yrs old ). We just told him off. The behaviour stopped. However- despite girl cat being smaller, she always got her own back usually by jumping on her brother from a great height about 10 mins after he had attempted to do his thing to her.
Just tell him off sternly when he gets frisky with her. They grow out of it eventually.

Cats have no moral compass do they ?

No moral compass what so ever. Ive tried skooshing water and they both look at me as if to say and what!?
I never considered spraying and or fighting so thanks for mentioning that!
When we see him do it we shout a stern no and clap our hands but it never works! As far as I've seen shes never done any tail thing but maybe she is. They're complicated creatures!!