How do I stop Brahmins from coming into my structures in Fallout 4?

This might not sound like a big deal but it's driving me nuts. A number of my settlements have Brahmins wandering around inside buildings, getting in the way and generally making a nuisance of themselves.

An example is Hangman's Alley, which must be one of the smaller settlements but because of it's excellent position I've put a lot of effort into developing it. I've built a multi-story structure that's partially open on the ground floor (as the existing environment means I can't wall it up).

Every time I visit Hangman's Alley there is a Brahmin stomping around on the ground floor of my structure, blocking the stairwell, making it difficult to use the workbenches, standing on sleeping bags and generally getting in the way.

I then built a Brahmin drinking trough at the other end of the alley, and built a fence (with a gate) between the trough and the structure. But that hasn't changed anything, the Brahmin hasn't gone anywhere near the trough and was still blocking access to everywhere I want to be.

So I shot it, dead. Which sort of solved the problem - I could now get to the stairs/ use the workbenches - apart from the aesthetic issue of having an immovable dead two headed cow in my bedroom.

After a couple of game days adventuring I returned to Hangman's Alley to find the dead Brahmin had disappeared and there was now a live Brahmin back in the ground floor - blocking everything off. Argh!

I tried herding it by pushing/ hitting it (didn't work), I tried to build another fence - but space is very limited and I couldn't build a fence/ gate/ door system that'd allow me and the settlers access the structure while blocking the Brahmin. I've also seen Brahmins jammed in doorways/ entrance ways so I wasn't sure how effective a fence/ gate/ door would be if I could build one.

As I said, it probably doesn't seem like a big deal but it's driving me nuts. I haven't put hours into building my settlements to have noisy ugly two headed cows stomping around and blocking access to my bedroom/ storage/ workshop/ stairways. Not too mention the up close animation for Brahmins is pretty shonky with lots of clipping which makes the whole experience worse.