Creative uses for Arcane Lock?

[Segev]

You can use it as a counter for many variations of the room filling with sand/gas/water, etc. If you plan to do this, carry around some thin boards with doors drawn on them. Place them over the flow of whatever you don't want there, and cast arcane lock. It should seal the gap. In a pinch, this can also be used to keep a ship from sinking, or to limit the flooding to one room by creating an impassable bulkhead.

I'm not sure arcane lock improves the ability of a barrier to keep things that normally permeate it from permeating, and I don't think "drawing a door on it" makes it qualify. Either placing the plank over the opening makes it "closed" or it doesn't. But again, nothing in it says that a "locked" entryway doesn't let water/gas/etc. through. Only that it cannot be opened. (And if you argue that it's open if it does let those things through, it's not a valid target for the spell.)

Arguably... it can also be used as an open lock spell on any magically sealed thing. You are able to open the object normally. That of course doesn't help with a lock- but a portal that only opens with a password or a key, or some other magic seal should be able to be circumvented.

"Open it normally" doesn't change how it "normally" opens. If it "normally" opens with a special key or password or the like, you merely can use that special key or password or the like to "normally" open it. You want knock to bypass that.