Kingdom Rush Frontiers

I got this achievement without building any guard barracks. Only artillery, archers, and mage towers. I used Alric as my hero as he can block the Dune Terrors (burrowing enemies) really well.

Don’t worry if you can’t get this on the first go around. Come back after you upgrade your towers and level up your hero.

I’m not sure if the worm comes up once per wave or maybe every minute or so, but after it does you can safely use reinforcements if you need to, to assist your hero in blocking. I got this achievement on casual and didn’t lose a single life. Just be careful not to use reinforcements if you haven’t seen the worm for awhile because they will get eaten. Also, I’m not sure if Alric’s sand warriors count since they’re a summon, not a soldier. None of them got eaten when I did this because they move on in tornado form looking for new enemies so the worm never grabbed them.

Make sure to move your hero out of danger, don’t use barracks, and don’t overuse your reinforcements and this achievement is fairly easy.

I tried twice with Alric but his sand summons were eaten, so I've switched to Didra, made 1 barracks and bunch of other towers, places hero at some range behind and units from barrack somewhere in front. Every time the work appeared - I moved units to another place, so nobody was eaten and finally achievement popped.