they had people attempting such when they prototyped in San Diego. I don’t recall anybody attempting to shimmy between or using the gaps as I picture you’re suggesting ... my thought is in the model that POTUS has ended up on, the pointed steel spikes, I don’t believe the space between them is adequate for those purposes, though you could use a rope or assembly like utility pole climbers use. But one of the big issues here is that, regardless, whether it’s tunnels underneath or clever ways to get over, you’re narrowing the means + opportunity for entry down to manageable + discernable times + locations, that goes a long way toward the goal + objective :)
I’m sure this has been said, the slatted design is so BP can see on the other side, to see if they are tunneling or have a crane or whatever.