Underground Base is the third stage in Alcatraz.
Le'boin appears as the main threat.
Squire Rel appears as peons.
Owlbrow appears as support.
Slowly build up money by stalling the Le'boins as much as possible. Once you have enough, spawn Bahamut Cat to kill the Le'boins. A little after the initial wave of Le'boins, Owlbrows will start spawning along with one Le'boin. Keep stalling them and send out Titan to resist most of the attacks and to directly attack the 2 enemies. Continue this strategy until you win.
Strategy 2 by Okreally
Cat lineup: 5 meat shields, Paris Cat, both Titan Cats, Shadow Akira and Dragon King Vars.
Spam all your meat shields straight away and an occasional Paris Cat to keep the Le'boins as far back as possible while you save up for Dragon King Vars. Once you are able to deploy him, keep spamming meat shields and he should take care of at least 1 Le'boin within a few hits. That will give you enough money to send out Shadow Akira and all your other cats. After that you just need to keep spamming whatever is available.
The Titans are good in this level because they are able to withstand the Le'boins attacks long enough to get a least one good hit in so if this strategy doesn't work for you, try keeping them and switching out your heavy hitters. Bahamut didn't work for me at all.
Strategy 3 (for 4-star difficulty, but tested in 3-star)
Lineup: 4 meat shields (including Jiangshi Cat,) Paris Cat, Ururun Cat, and Bahamut Cat (Li'l Nyandam is recommended but not essential), Li'l Dragon Cat (optional).
Power-ups: Rich Cat, (Cat CPU is optional.)
One can simply build up money to about 10000 units and spawn Ururun Cat and Bahamut Cat, using Paris Cat to snipe the squirrels away if they get too close. Simply spam units to win in what will be an excruciatingly long battle. One might swap out the Li'l Dragon Cat for Prisoner Cat, but it's not essential to the success of this strategy.