PLEASE DO NOT SHAVE, CUT, or TRIM YOUR DOGS'S DOUBLE COAT!  
Shaving or trimming your double-coated dog causes irreversable damage to the hair follicles.  The coat may not ever fully recover from this damage.  "Shavedowns" or "summer-cuts" should only be considered as a last resort option for medical reasons, or if the undercoat is severly matted making removal impossible.

Normal healthy double-coat

Normal healthy double-coat

Each normal and healthy hair follicle grows one topcoat hair (the pretty and silky hair that you see) with six undercoat hairs (actual number varies by breed).  The undercoat hair is very kinky and frizzy and serves to seperate the top coats hairs from each other to provide optimal insulation in both hot and cold temperatures. With a healthy coat, you normally should not be able to see any of the undercoat fur.
What happens when the hair is cut?

What happens when the hair is cut?

Cutting the hair at any length causes the hair follicle to be stimulated to re-grow hair.  The problem with this is not that the topcoat re-grows to its original optimal length, but the undercoat doubles in amount! 
Double the undercoat!

Double the undercoat!

Now there is only one topcoat hair with 12 undercoat hairs. This begins to compromise the insulation to the dog, doubles the amount of shedding, and negatively affects the dog's skin and coat health.
  
Cutting the hair again = 3X the problem!

Cutting the hair again = 3X the problem!

Now, you cut the haircoat again.  This now tripples your problem!  You will have tripple the hair, tripple the shedding, and very little of the pretty topcoat left.  This leaves you with a frizzy dog with terrible insulation from the heat and cold and very poor health of the skin and haircoat.  

 
Severe damage to the hair follicles & coat!

Severe damage to the hair follicles & coat!

The over-grown undercoat will begin to mat close to the skin preventing your dog from any escape of body heat.  This is now a dog that potentially can die of heat stroke! Now a "shavedown" or "summer-cut" is the only option left. The matting of the undercoat also occurs if proper removal of the shedded coat is not done twice a year as soon as it is shed. This situation is easily eliminated by not cutting your dog's hair in the first place and by proper removal of the undercoat durring bianual shedding seasons.

Breakage of the topcoat can further stimulate the hair follicle to grow more hair.  The new hair growth is not able to penetrate through the matted hair which now can cause severe damage to the hair folliclle.  If the damaged hair follicle is not addressed, this can further cause perminant balding.  Please let us help you to maintain the health of your double-coated dog's skin and haircoat.