Combos are nearly impossible because the snails will spawn further away than the bucket can move to in time. Faster bucket or a calculation in the snail dropping script to make it possible to reach snails in time.
When I hack my xp so I can pump up a drone sufficiently that my salvaging is over 2000% you'd think the indomitable and invincible achievements would be easily attainable, and yet they're still impossible. You might want to reconsider the way those two achievements work.
Achievements are supposed to be skill based, not "Hey, you won the lottery".
You can get both those feats on the endless modes, especially if you keep going to level 20 when things start getting really crazy. I've also gotten them on sector 38-39. So it's not impossible. =)
If you're on chrome type chrome://plugins, and disable chrome's integrated flash by clicking on the details button, then click the disable button in the version of flash that contains /PepperFlash/ in it's directory link.
 "Madness Hydraulic"){kind=icon}
 "Pingy the Ping Idle RPG"){kind=icon}
 "Mummy Mojo"){kind=icon}
 "Diggy"){kind=icon}
 "Zombo Buster"){kind=icon}
 "Skills Idle"){kind=icon}
 "Betty IX"){kind=icon}
 "Asterite"){kind=icon}
 "Amber Helix"){kind=icon}
 "Spurt"){kind=icon}
 "Bush Whacker 2"){kind=icon}
 "Battle without End"){kind=icon}
 "The Last Stand: Dead Zone"){kind=icon}
 "400 Years"){kind=icon}
 "The 'Iron Grip: Warlord' Flash Game"){kind=icon}
I'm happy that you enjoy it. =)