Of course, given that the Dominion likely had agents on the other end by then the odds are they'd have just found out how to deactivate the minefield themselves and done so whenever they wanted rendering it useless as a deterrent.
That, and something else to consider.
We never even saw ALL of the full military might of the Dominion. The show always implied that if we HAD seen said full might, they
still might have been a match for the combined forces of the Feds, Romulans, and Klingons. The war proper didn't start until the very end of season 5; provoking the Dominion with something like a cloaked minefield was best put off until it was absolutely necessary, when a war seemed completely unavoidable (and, as Sisko put it, had become their "only hope", meaning that at that point, it was clear that a full-on Dominion invasion was looming). Before that point, they probably held out some small hope that a full-scale conflict could yet be avoided. That hope may have been unrealistic, but having either the Klingons or Romulans on board as a military ally for any extended length of time (let alone
both at the same time) was not something they could count on maintaining, and the Feds knew that on their own, one military vs. another, they would lose against the Dominion. So they put off a war as long as they could.
Don't forget, also, that the Feds like to avoid war, in general, as much as possible. Even when faced with a power whom they could comfortably beat down in a full-scale conflict, they will take any reasonable diplomatic avenue if they can, preferring to avoid the loss of life that would occur in a war, even if the majority of those lost lives are not Federation lives. This would be true with regard to both the Dominion and the Romulans. Frankly, I thought they took it too
far at times; the Romulans gave them more than just a bloody nose at times, with little real response, but as others have pointed out, some of these incidents went down without any real proof of Romulan aggression, so it could have been politically murky for the Feds to retaliate for them.
And a series about two sides constantly in a "Minefield" arms race of making a better minefield until the other side just finds a way to trash it, isn't dramatically viable for 5 seasons.
Perhaps they would have deactivated the minefield. The point isn't that the Dominion would have succeeded (and i'm sure they would have to, in order to have a Dominion war), the point is, that "in-universe", the absense of such measures makes our heros (and Federation/Bajor at large) look like having all the smarts of the average brain-dead lemming. As in none. They are idiots. Utterly incompetant fools.
And while the argument that such a minefiled solution would have made the series dramitically unviable is interesting and may well be true as there was something to be said for the Dominion always able to pop out of the wormhole without warning, it isn't relevant to the "in-universe" argument.
To be honest, I've never understood this mentatily, of actually concluding that what I bolded is true in-universe. Out-of-universe elements - writer intent, writer mistakes, budget limitations, etc. - MUST be considered, even in an in-universe argument. The reason is because the show ISN'T real. It's not a documentary or historical fiction, it's entirely 100% made-up.
When the show presents us with the notion that Data is leagues more advanced than any real computer system, then some dialog has him getting some intermediate math wrong, we have two choices:
A) acknowledge that the show isn't real, that a writer made an error and no one caught it, and say "If it were 'real', Data would have gotten that right, because he's freakin' Data."
B) say "writing goofs have no bearing on in-universe events. What 'really' happened in-universe is that the super advanced android got that math problem wrong, and none of the trained Starfleet officers participating in the conversation caught it."
Going with B) (which, in the context of this minefield/military competance issue, would mean saying "The characters in-universe are idiots") would mean I can't take the show seriously anymore. I don't want to watch a show about idiots. I'd rather assume that there are other reasons in-universe that we may not be aware of for why they didn't put up a minefield.
And here's another thought: Perhaps the technology to create self-replicating mines wasn't viable until "Call to Arms". Don't forget that it was Rom who came up with the idea, in a flash of random insight; this (and Dax's initial "wat?" reaction) suggest that the tech involved may have been experimental or obscure. And given the size of the wormhole, and the complexities introduced by the fact that it was a wormhole, not just a planet or something else mundane, that they were trying to mine, it was quite a challenge: O'Brien and Dax went through several other ideas in that scene before Rom suggested self-replication, and they shot each idea down for one reason or another. So before this, any minefield they attempted to put up may have done literally nothing except aggravate the Dominion.
Is there evidence to suggest they can?
There was already one Romulan War, I don't think anyone was ultimately eager to have another.
From TNG's "The Defector", Admiral Haden to Picard re: Romulans:
"No one here wants a war, Captain. But we are prepared to take them on if that is what they want."
That doesn't mean that the Feds
would necessarily win an all-out war with them, but this statement would not have been worded that way, and delivered with that level of calm confidence, if they weren't at least a good match against them overall.
