Need help with a B/W Human Detain Deck

So are you only interested in using cards you already have or would you be willing to spend a few bucks on some singles?

I think the detain strategy works just fine for casual play, but I would suggest thinning the deck down to fewer different cards and having higher numbers of the ones that will really work for you to increase consistency.  For instance, drop Delver of Secrets (you don't have enough spells for him to flip reliably), Moorland Inquisitor, and Midnight Duelist - none of these really help your scheme.  If you're in need of flyers, Judge's Familiar is a guaranteed flyer and can counter something big.  If you're after first strike defenders, since you're not limited to format, White Knight or some added Precinct Captains provide first strike without the added cost.  If you're in need of protection against vampires... well... try garlic? 

Really though one of the hardest lessons to learn is to rein in your imagination a bit with the cards to focus on one, two, or at most three things the deck is trying to do.  Then the challenge is finding the cards that will best achieve those limited goals and to do so consistently.  This means largely avoiding cards that are 1-offs in a deck (and frequently cards that are 2-offs as well).

That being said, cards to increase the count of in here that you've already found include:

Azorius Arrester, Deputy of Acquittals, Precinct Captain, Fiendslayer Paladin, Lyev Skyknight, Feeling of Dread, Inaction Injunction, Bonds of Faith, Martial Law, and Azorius Guildgate.

Cards you could easily lose and wouldn't miss a beat:

The three creatures I listed earlier, Intrepid Hero, Master of Diversion, Quicken, Frost Breath, Ring of Thune, drop ONE Door of Destinies, Burden of Guilt, Forced Worship, Dismiss into Dream, and several lands (ideally you should run somewhere between 20-25 lands depending on the curve).

Some cards to consider picking up to put in here:

Archon of the Triumvirate as a 1-off (you won't get that high mana-wise most games), Lavinia of the Tenth, Hands of Binding, the afore mentioned Judge's Familiar, Detention Sphere, Azorious Charm, Imposing Sovereign/Blind Obedience, Champion of the Parish.

And if you're just up for some added shenanigans, Venser, the Sojourner could be fun.

Anywhom, what you pick up will depend on what you're willing to spend, but know that there are options.

Best luck!