You're either exceptionally gullible or really bad at convincing other people of your bullshit.
The largest spider in the world is the Goliath bird-eating tarantula, which is large enough to take down small birds with relatively considerable effort (it can eat birds if said birds do not pay attention to their surroundings and are either very young or very old, as a physically fit bird can rip a Goliath bird-eater to fucking shreds with only a little bit of damage to itself), but it primarily feasts upon insects (like pretty much all spiders do). This, the largest spider in the world, is not large enough to take down even a fucking chihuahua.
The largest spider in Australia is the huntsman spider, which is still too small to eat any kind of dog or cat (at their peak, they can eat small geckos, but again they mostly subsist on insects because insects are fucking stupid and are much easier to catch).
Assuming you are in fact just a gullible retard, you're probably referring to the "Angolan Witch Spider" hoax that circled around the internet a few years ago that was based around a fairly shitty Photoshop of a sized-up wolf spider on the side of a house (which, by the way, is probably where you got the burrowing aspect, because some wolf spiders tend to burrow and wait for prey). It was debunked rather quickly and most people only believe in the "dog-eating spider" when they're pussies who are terrified of the mere concept of a spider.
Use your goddamn brain and think about it from a fucking spider's perspective: which is an easier meal, a yapping little Shih Tzu that will put up a fucking fight and probably break a couple of your legs at the minimum, or a bunch of bugs that will literally wander right to your face?