That Fencing Issue, and Why
That Fencing Issue, & Why is it necessary? 
BECAUSE you should give your pet what he/she longs for due to inherited traits. That is to be outdoors without being constrained. But they can't run loose either. So, what to do?

Scotties were bred to love the outdoors, and they were bred to explore looking for varmints in the highlands of their ancestral country. Since we have made them pets, and we now live in busy cities and towns with cars and roads that kill. Even a country road has an occasional car, and if the car and the dog meet, it is always the dog who is the loser. Never happened to your last one? Well, that is simple luck, not always the end result for the next. 

A Scottie puppy needs social development. It needs to explore if even a small area, sniffing, enjoying the sunshine and the joys of good old Mother Nature. It should be part of every puppy's life. Sure, he can play indoors, but not with that same result. 

Now, I am not saying, throw the pup outside and forget he is there. You do have to be very vigilant always. Be sure to padlock a gate, so that it is never left open. Be aware in the south that there are snakes and hawks. Be aware that a Scottie is a digger, and can work his way out under a fence.

Terrier comes from Latin terra, meaning earth. Scotties love the earth. A carpet, wood or tile floor is just not the same. 

Why not take your Scottie walking so he can have these experiences? 
Well, you can, but what do you pick up from your neighbor's lawn? 
Pesticide residue, worms, fleas and ticks, to name a few.
If you walk your dog, your neighbor won't like your dog doing his business in his yard either.
So, walk your Scottie for exercise, not for exploring. Let him explore your own yard, that you know is free of the poison and parasites.

Do you have to fence an entire yard? NO! provide a partial area. Enclose an area off a back door, or enclose a patio. Here's a photo with an idea.

What about electric undergound fencing? 
Not a good idea for a Scottie. They must always wear a shock collar. 
If they see a squirrel, neighbor's cat, or smell a rabbit trail, the motivation to chase is great.
Scotties can endure a lot of pain. So, through the electric barrier they go, shock and all.
Once through, the motivation to come home will not be very great, and the temptation to go exploring is going to lead them far away from home.