Theres a couple things you could help out with first, that might make designing a macro set for you easier. What type of macro do you use on your shamans for normal play? one button dps spamming pretty much i imagine correct>? one button for aoe and single target? or 2 separate keys one for aoe one for single?

Dk tanking relys quite a bit on gear, spec, and glyphs. What spec do you want to use>? Do you KNOW how to play a dk? ie do you understand rune mechanics(rune refresh rate, death rune creation/consumption/usage)? Do you know what a runic dump is? (>>>INSERT PERVERTED DISGUSTING JOKE HERE<<<) lol

If you use a spec like i do(taking the two talents that give you death runes, one from the blood tree, one from the frost tree) and using the glyph of death and decay, death of howling blast, and the third glyph i usually use is rune tap(*because i use that skill on all 3 of my dks for party heals on my team) but my third glyph choice for normal frost tanking use is glyph of frost strike.
the basic macro is as follows(keeping in mind i have no clue how click macros work given my setup of addons/bars/stuff)

i suggest leading off with death and decay on every pull. this is to be put on a key separate from every other key. DnD creates a royal shitton of threat but it doesnt help in the making of death runes which is kinda super important for single target threat gen. Dks icy touch skill has a super duper high threat modifier and the goal to threat gen on ANY single target fight is your ability to spam it as fast and as much as you can. For single target you dont really need to use DnD to pull, though it works well as a starter, you WILL have to roll into your rotation a little bit and spam your tank macro a couple times before you load your shamans up and start spammin the dps key.

Since i tend to use my mouse to move forward, and one of my buttons on my mouse is my /toggle autorun key i unbound my W key from move forward. I put my tank macro on my W key and spam that while positioning mobs/my tank before i start my dps.
I'll put in parentheses what runes each part of the cast sequence uses so you can better follow the two button system( runes and runic power usage) technically you'll need 4 keys for tanking. An aoe key, a single target key, a runic power key, and a key for dnd ********edit sorry, you may need a fifty key, for howling blast procs ******

lol i hope you're not confused yet!

/target focustarget **i use a focus as lead system for my set up, you can use ftl just delete this line**
/castsequence reset=combat howling blast(UF),plague strike(U),Pestilence(B),Blood Boil(B),Icy Touch(F),Obliterate(UF), Obliterate(UF)(** at this point when all your runes refresh you should have a frost , unholy and 4 death runes, Using One howling blast, 1 pestilence if the free howling blast didnt proc from obliterate/rime talent, then 3 blood boils), Pestilence(B), Blood boil, blood boil, blood boil
/cast !rune strike

this is the aoe rotation(above). If it hangs up, use blood tap to convert one of your blood runes into a death rune, or use empower rune weapon to reset it. At any point during your spamming of this dps macro it hangs up and all your runes are still on cooldown, you should have runic power made and casting Frost strike on your runic power key is what you should do. Casting howling blast whenever you can (as rime will proc a free one on occasion for casting obliterates) CAN MESS UP THE MACRO, but it shouldn't given the time delays in the ability usage, IE howling blast resets every 8 seconds after you use it. with all your runic dumps and the other skills in between when howling blast lands in the macro you should never run into conflict, but it CAN happen it shouldn't but nothing is perfect lol.

some minor advice when it comes to DK tanking, especially as frost. OMFG take all the + hit talents from both the frost and unholy tree, and stack hit on gear as much as you can until you reach 10 % +hit (around 318 rating)on your character sheet. ALSO, stacking EXPERTISE is OMFG important for multiboxing, ESPECIALLY as we're using cast sequences. The cap for expertise is 24 on your character sheet to push dodge/parry off the chart from behind. HIGHER is potentially wasted, but if you can find gear with it, use it. My tank set averages around 32 expertise. MISSING JUST ONE ATTACK can throw off the WHOLE rotation/macro. It sucks, but unless you do the click macro thing its something you have to live with.

Now for a cast sequence for single target

/target focustarget
/castsequence reset=combat Icy touch, plague strike, Blood strike, blood strike, obliterate(*runic power dump press your other keybind !!), Obliterate, icy touch, icy touch, icy touch, icy touch, Obliterate,blood strike, blood strike, obliterate, icy touch, icy touch, icy touch, icy touch
/cast !rune strike

the idea behind single target tankin is to cast obliterate and icy touch as much as you can. Obliterates and blood strikes if you're specced right turn your runes into death runes. Death runes can be used as any kind of rune, and icy touch is the most threat per use ability we have next to death and decay, but death and decay doesnt generate enough threat that it will work for sustained threat vs how icy touch does so we go for broke casting it

Everything should be good to go as is, remember to use your runic power dump for frost strikes whenever you dont have runes up.