Help on ‘guard’ dogs!

Hi everyone! First post in this sub 🙂

First of all, thanks to all the mods and posters here, I was super nervous on seeking advice on this and getting responses that might be harmfull to the pups, but having read the rules and some posts here I'm feeling super secure! Awesome comunity, haha <3

For some context, the area where I live is becoming increasingly more dangerous, ie home invasions (for theft). I've had dogs for 'protection' since I was little, but the circumstances this time are a little different. I've had 3 GS's (2 households) that were great for what I consider guarding — barking at strangers and being scary looking for long enough to scare people off/for me/family to do something, and still being socialized. All of my girls would stay alert and bark at strangers, but never bit guests when they were with family. None of them were professionally trained, and honestly It's a super lucky streak, our first girls in each household were great, we worked with them for what they needed corrected, and they passed that to the others.

Now, I have one of those 3 GS's, a senior lady, and another adult female. The new female barks alongside our senior, but is too much of a sweetheart to do anything on her own. Since my family and I don't believe in the common training methods for protection dogs and don't have access to professional alternatives, we've been thinking of getting a new puppy of a bigger breed (mostly livestock guardian pups of mountain-y regions) while our senior is still with us, but were not sure if she could handle a new puppy — I don't think she'd harm it, but I'm scared It'd be too much energy for her to handle.

We've been thinking of a bigger breed for the 'scare' factor and the hope that the personality will hold up to their name, haha. Ofc, the puppy will not stay alone with our senior until we're sure about it, and we will properly introduce them and hire professionals if needed.

I know I rambled quite a lot, but my question is, could this work without too much stress on our senior? And if not, what is the alternative without fear or punishment based training?

I'm fully aware this could be a gamble, but with the success we've had in our family, could it be worth it? Tysm everyone! Feel free to ask questions or scold me in the replies!!