Burrows would be nice, but they are not necessary. Just design your forts so that the defensive systems are mainly outside. For example my fort uses an large castle structure outside as its entrance, it is backed up against a mountain hill with a high vertical slope behind it (which I cut out of the mountainside), and a 3 sided moat to the front. It uses 3 drawbridges, one for the exterior moat, and 2 for the interior (one is used to divert enemies onto a winding path. The fort has 4 towers, one on each corner with fortifications all around and a roof (so that no one can snipe from above on the hill). the wall only has fortifications on the inside to shoot at enemies on the winding path. I also made the inside of the fort floodable with pumps (and drains) to drown small armies in. I didn't bother trapping the inside of the fort though, just the outside around the first drawbridge. The ramparts can also be sealed off with a lever deep inside the fort. Oh and the moats can also only be accessed when the bridges are down (3 tile wide moat with stairs in the middle beside the bridge)
So if a siege comes i just order all the dwarves inside, and let soldiers go outside into the ramparts and towers. Even if the enemy could bypass the castle, the entrance is a long tunnel with a ramp going down towards the end, this ramp gets covered by 2 bridges on each side, and a portcullis in front of it, beyond the bridges is 4 masterwork ballistae behind heavy fortifications that overlap and cover the 4 tile wide passageway.
Nothing is getting in the front door unless I let them
Anything else will get drowned, shot to bits by crossbows, or splattered by ballista bolts.
The secret entrance is also pretty secure though not as fancy, but the passage way in is flooded to be a small "lake" when not in use (that is what makes it secret, as the lake is drained and refilled as needed).
Beyond that I keep careful tabs on exterior jobs and tend to do them in large batches for safety. Technically though there is no reason to ever open the gate other then to trade. Water comes from an underground river (which is also fully secured), wood comes from underground tower cap farms (the only wood real dorfs use), and orders are set up to keep stupid dorf wandering into ambushes to a minimum.
But then I am very security minded.