No kidding!
The first massive cut I got was in the sidewall of a nearly new Marathon Supreme, in the sidewall.
Only thing I had for a boot was a piece of old inner tube, which bulged out the side, nearly catching the brake pad, for the 22 miles home.

After that, I bought a pack of the Park TB-2 tire boots.
They are reinforced so they can't stretch/bulge, and have adhesive to keep them in place.

A few years later, I got another massive slice (in the sidewall again).
It was large enough to put my thumb through it, and I was positive no boot would hold.
But since it was a 6 mile walk home, I pulled out the Park boots and gave it my best shot.
Incredibly, the boot worked perfectly and got me home.