If someone is trying to shield camp you, a good setup to eat half their shield or more is:
Get a galaxian in hand -> plant hydrant -> throw galaxian as you're falling off of hydrant -> fair hydrant -> run with both of your projectiles
The closer you plant the hydrant to them, the better. They'll probably start shielding the moment you come remotely close.
The galaxian thrown from hand can't be stolen, and if it and the hydrant touch their shield, that's 21% assuming the galaxian only hits once. That's 4% from half of the shield gone immediately, and that's not accounting for the time they're sitting there with shield up.
You're free to do whatever for more pressure. FH Nair will do 10% more to it while keeping you very safe, or you can use auto-phantom fruit (galaxian is out, so it's going to happen) mid dash to go into an F or Dsmash. If the galaxian hit twice, I'd go for the Fsmash to attempt a shield break. That's 13% (launched hydrant) + 18% (2 galaxian hits) + 16% (Fsmash) = 47%, most likely a broken shield.
If they get out of this without %, I assure you their shield will be hurting. Drop another hydrant, Fair launch it ASAP, and continue chasing them down.
Edit: If you can get a Key in hand, get on top of them and Zdrop Key(15%) -> Hydrant drop (9%) -> Hydrant launched from Key (13%) + Bair (12%) = 49%, which should be a broken shield unless they powershield something.