Eating Poop and other Sundries

Hi, I need some advice. This is actually for Kaya, my malamute mix, so I hope it is okay to ask here.

Kaya is 100 lbs, 5 years old, and eats 2 cups of quality food a day to maintain her weight. I used to feed her according to package instructions for a dog her size, but after spaying her at 18 months, she turned into a blimp. After a year and a half of being a hog, I changed to a higher quality food, cut her back and made her lose the weight. She actually eats the amount that the food recommends for a senior/sedentary dog. She stays a healthy weight on this amount, and I have feed her Canidae, and recently, in the last two weeks changed over to Eagle Pack Holistic Lamb and Rice with Oatmeal. Here's the problem. She has always LOVED her food. I have to put large rocks in her bowl to slow down her eating or she'll eat the whole two cups in about 30-45 seconds (not kidding). With the rocks it takes her about 2-3 minutes to pick out all the food. (they are big rocks, she can't eat them).
Well, I caught her about 2 months ago eating her poop (never noticed her do this before). Since then, she's been doing it with frequency, plus eating the walnuts that are falling off the black walnut trees along the back of the property (which worries me because I understand these are toxic?). She has eaten nuts before here and at another place we lived when she was a puppy where there were acorns. Heck, she was wrestling with Odin, yanked off his safety release collar (all this about 5 weeks ago) and ate it. I know this, because I found the chewed apart nylon collar in her poop about 2 days after it disappeared off his neck! (I still don't know where the 3 tags are that were on it )
She is regularly (and recently) dewormed. I supplement her food a couple times a week with deer meat. But I am wondering if the amount I feed her just isn't enough to keep her from feeling hungry. Should I give her some filler type additives to help her feel more full without making her fat? If so, what?
I just really do not want her eating her poop. Yick! I can't stop that since she loves to be outside and spends a lot of time outside in the yard without me, so I don't always know when she goes.
Advice would be much appreciated.

I would love to hear more about the black walnuts, my dogs love to eat them too and I am outside picking them up daily to prevent them from getting them.

Poop eating is called coprophagia and here's some info on it: http://www.sniksnak.com/doghealth/coprophagia.html

Perhaps to add to the volume of food your dog is getting you could try adding lots of raw veggies. Carrots, green beans, sweet potatos, etc. all provide fiber and volume without many calories. They will also require chewing which might slow down his eating as well. We use the raw veggies as treats too. They especially love green beans right out of the freezer! Worth a try.

That's a good idea to feed vegetables. Maybe feed her twice a day if you don't already. Shouldn't potatoes be cooked first, though?

I read somewhere (probably in Dog Fancy, Bark, or National Geographic magazines) that walnuts are toxic to dogs because of a fungus that grows inside the shell. Acorns can make dogs very ill - we had lots of problems in the past.

Hi, thanks for the advice and links. Pixie ate poop, too and I never could break her from eating other dog's poop, though those potty mouth pills stopped her from eating her own. I think I will start adding the veggies to Kaya's food to see if that helps.

One of my husband's friend's shepard husky mix use to eat her poo. He was mixing pumpkin in. I have also heard that pineapple makes it taste bad.