How to secure Grub control from other distro?

[znavko]

Hello! I have two distros on my PC:
on /dev/sda - Guix
on /dev/sdc - Ubuntu

Today, after update and upgrade of newly installed Ubuntu and also after 
installation of lubuntu-desktop and lxde on ubuntu,
I was unfortunately grieved.
Lubuntu had recovered my Grub and had broken everything!
I was need to boot into Guix with grub command line and make `guix system 
reconfigure /etc/config.scm` for to get my Grub
controlling by Guix again!

I have a question. Have I any possibility to secure and save my Grub from other 
buggy distros i may setup on other ssd in my pc?

I think it will be hard to fight with ubuntu or debian or some other distro not 
to touch Grub.