Yes it did. But the alternative border would have been a unified Korea with the north’s leadership in charge. Whether that is worth the trade off depends on your politics I suppose.

Or a tight border for some years and than a reunion like in my country, germany?

(even though there were mines on that border, too, but in a limited way that there are no more traces of them today)

Anyway, I am still highly sceptical to the claim, that mines prevented a total communist korea. Debating about that is not really constructive. Do you have studies for your claim?