Your hunters wont have made it because it can take a a surprisingly long time for a dwarf to equip himself for military service. Because of a bug/less than ideal implementation, a hunter will drop his xbow and grab a 2nd, different xbow, as well as a backpack and flask, which i think he will fill with food and water before finally heading to the location you specify. And thats without armour.
The dogs will help, normal dogs will attack hostiles unless they are chained. I would expect only 2 or 3 dogs to receive injuries or potential death from a single thief. When Ive used the pasture dogs over entrance tactics I usually go with about 8 dogs, and I expect some to not last very long at all. Also I find that often dogs cannot catch a fleeing thief and will end up chasing a long way from the pasture on a fruitless run.
I have read that hunting dogs have an increased range/ability to detect hidden creatures, but I cannot offer you any experience on that matter as I found it hard to tell the difference. War animals do more damage.
Easiest newb tip to keeping thieves and unwanted visitors out, keep the doors closed.
Build yoruself an "airlock" with 2 bridges leading from outside to inside and build a trade depot in there. That way the inner bridge can be sealed keeping you safe, the outer bridge can be left open to that incoming caravans have a destination and will not avoid your site with their wagons.
Once the cravan has arrived you can close the outer gate and open the inner gate, minimising (to practically zero) the chance of hostiles getting into your fort. This can be time consuming (you cant move goods to the trade depot with the inner door closed) and pathing to your airlock can take time depending on your perimeter walls, and caravanas especially multiple caravans with mutiple trade depots can be finicky but you can work out a reliable pattern and this is the best way ive found to do things so far.
screenie of the airlocked trade depot
http://imgur.com/sKC9BruI have 4 of those around my perimeter. Each 1 has a weapon stand that I can use to get my melee squad to train close to the site of an active trade so they can help out if necessary. Also above the airlocks is a floored area so I can have marksdwarves above the gates firing down. The entire outside wall is also enclosed with fortifications offering extra protection to any marks dwarves on the ramparts (and preventing them from "dodging" off the walls and into my moat.
One might say ranged is better for thieves as they tend to run away when discovered and as I mentioned dogs struggle to catch them, so ranged might give you a few "hits" on the thief that you might not otherwise have gotten. Also I would say marksdwarves are easier to equip and train, as well as being effective without large amounts of metal armour.
Definitely give your marks dwarves shields as well as xbows, even if no other armour is available.
After that its up to you. I often have my crack melee squad (consisiting of 4 males from my starting 7 that all had teacher and 1 useful military skill) siting in/around my open gates when I went to cut some wood outside or dispose of the last bunch of unfortunate visitors to my fort. I know from the 4 of them breaking several sieges they are almost untouchable. (I did savescum the death of one of them by a troll, I couldnt even find the combat log relating to his death.
In my last fort I had several (~4) squads of 5 marks dwarves and no melee dwarves. When a caravan arrived I was using marksdwarves to offer as much cover for a caravan as I could from the walls with 1 squad stationed above the open gate.
Hope thats helpful