Help! I keep breaking nail clippers

I have two very large dogs with THICK nails. I've bought all the top sellers on Amazon and a diamond bit Dremel-type nail trimmer. They have all broke or dulled. So much that they're useless. I'm not a groomer. Just a dog owner trying to do my best for my babies. We've worked very hard to get comfortable with nails. German shepherds are just the biggest babies aren't they? They are a lot better with the Dremel but it gets dull so quickly and the guards on them are literally not big enough to fit their girthy claws.

Please tell me your tricks or your favorite clippers/Dremels. I'm at my wits end. Ps. Thank you for all you do. Grooming is a thank-less job. You are incredible and make the world of difference to your clients & families. Thank you.