You Don't Want Walls, You Want Bait
Sure you want to have a 20ft high steel wall with a 100ft wide 40ft deep trench facing the exclusion zone to keep out the low-grade Kaiju. Or at least a fence to ward off humans who accidentally stray to far west. You might even want some strategically placed strongpoints for specialist troops/machines to sally from in the event a mid-grade Kaiju gets frisky. But what you REALLY want (Given that Godzilla is essentially unkillable and the high-end kaiju probably only slightly less invulnerable) is a way to get the Tier 1 Kaiju to GO ANOTHER WAY.
So you want Bait. Tunnels under your lines that stretch deep into the exclusion zone that are far to small for any sort of Kaiju, but which on short notice can pop out something that interests the Kaiju. The Bait then heads screaming in the direction opposite of your walls/civilian centers. If you want added spice, maybe have it head towards another known Kaiju in the hopes the monsters will kill each other off. These Bait machines also need to have SOME sort of Kaiju nourishment, so they don't end up getting viewed as inedible and eventually ignored.
Why tunnel-deployed? You don't want the Kaiju to view the Wall/end of the zone as a source of food. Thus you need some sort of underground system where the Bait inevitably appears BEHIND any Kaiju that hits X location. You'd want literally thousands of such tunnels so the appearance of Bait could be deemed random and you don't just have Kaiju "camping" the tunnel exits. For the same reason they need to be as hidden as possible. This also means that there needs to be essentially wasteland between where the bait arrives and the wall. So the Kaiju thinks "man that looks like a terrible place to find dinner" and makes going towards the Wall as unappealing as possible. So they get to the edge of the wasteland, a tasty snack pops up behind them, and they think "oh yeah, there's obviously better hunting in the West."
What Nourishment? That depends on the type of Kaiju. Worst-case scenario is they're manned craft. And lets face it, they are because "Kaiju bait pilot" would be a HELL of a main character. 121
Plus who knows how good your radio/satellite comms are. I'm envisioning some sort of ATV/mech/skimmer (tech-level depending) that carries a human crewman or two and a couple cows or a few tons of meat or radioactive elements/whateverelse a Kaiju feeds on in your universe.
The Plan Ensign <PERSON> is a KRV (Kaiju Redirection Vehcile) pilot, and it's his shift at Bastion 12 when a Primary Level Kaiju crosses within 50 miles of The Wall. Bastion 12 goes to Alert and Ensign <PERSON> mans his KRV and prays. at 40 miles to the wall the Kaiju officially enters the Redirection Zone and Ensign <PERSON>'s KRV is launched. Tactical command has set up <PERSON>'s KRV to appear half a mile to the Northwest of the Kaiju. The KRV appears, and sends up various flares/sirens/look-at-me devices. The Kaiju, naturally, turns. It sees the KRV, senses the meat/radioactivity/whatever inside, and pursues. Ensign <PERSON> now plays the dangerous game of trying to stay in front of the Kaiju and unkilled for either A: as long as possible, or B: until he reaches some arbitrary distance from the Wall far enough away that the Kaiju won't just turn around and be back in an hour. The chase might last days, it might last hours. Hell it might take weeks! (No idea on your Kaiju speed.) Eventually though the jig is up. <PERSON> ejects. The pod punches him clear of the Kaiju, who pursues the KRV, kills it, and feeds. Ensign <PERSON> now must face the treacherous Exclusion Zone and potentially other Kaiju to return home, and/or <PERSON> is killed by the Kaiju and his family gets a "Deeply Regrets" telegram.
(Sidenote: you could also have tunnels like 200 miles away where KRVs could dive into and escape Kaiju, but that's a whole other problem of "do the Kaiju dig after it" "do the Kaiju now 'camp" the escape holes" etc. etc. running-hopefully-ejecting-hike-back seems like the best of bad options to me at this point.)
You could also have some sort of airborne recovery teams to rescue ejected KRV pilots. 837