@gtbrien,
												gtbrien wrote:"Praise to our gracious and merciful God, our strength."
"Laudamus ad Dei comis et miserecordis, fortibus nostris." 
 
Let's start with "Praise".  You have translated it with the Latin for "We 
praise".  If that was your intention, good.  Other ways include
Laus -- The noun "Praise"
Laudate -- "Praise" as an imperative 
Laudemus -- "Let us praise"
If you want to use the noun 
Laus, then the form of 
Deus to use is
 Deo 
(without the preposition).
If you want to use one of the verb forms, then use 
Deum as it will be the 
direct object.
As for "gracious and merciful", I would follow the example of the Latin 
Vulgate bible and use the adjective 
clemens for "gracious".  So:
<noun> 
Deo clementi et misericordi
<verb> 
Deum clementem et misericordem
I would use 
fortitudo for "strength".  It should agree in case with 
Deo 
or 
Deum.  So:
Deo . . . fortitudini nostro
or
Deum . . . fortitudinem nostrum