I also agree on the food. If you are going to give dry food for part of his diet, check the ingredients list and ensure meat is high on the list of ingredients - in the first couple of spots preferrably. That way the main ingredient is meat rather than fibre filler. I get IAMS for my dog.
I buy fresh meat for my dog from a pet butcher - they don't put preservatives in the meat. It costs around half the price of meat you buy for human consumption. Whether you give raw or cooked meat is an endless debate - at the end of the day, just make sure it's good meat with not too much fat in it. If I buy meat from the supermarket for the dog, I cook it and pour away the juice which hopefully also gets rid of most of the crap that they put on the meat.
I tend to cook all my dog's meat because it lasts longer in the fridge whereas raw meat needs to be used sooner.
Vegetables are not essential but are very good for your dog as well (about 1/3 of their diet max), but you need to steam it or if it's raw mush it up in a processor. Dog stomachs can't process chunks of vegetables very well as I recall. My dog prefers pumpkin, sweet potato and zucchini. Different dogs like different things.
Rice, pasta, and similar aren't of much use to your dog - their stomach's can't process those sorts of foods.
Yes, this.
@Nikki: So I guess getting Beneful was a bad idea? The lady there said it would be perfect for my dog, and not knowing beforehand I couldn't say no. I will be getting Royal Canin from now on.
Beneful isn't the best. I can't find the ingredients online, so take a look at your bag. Is it like ground yellow corn, cornmeal, soybean meal, brewer's rice, etc? If so, that's bad.
Here's the ingredients for Chicken Soup for the Dog Lover's Soul:
Chicken, turkey, chicken meal, ocean fish meal, cracked pearled barley, whole grain brown rice, oatmeal, millet, white rice, chicken fat (preserved with mixed tocopherols), potatoes, egg product, tomato pomace, duck, salmon, flaxseed, natural chicken flavor, choline chloride, dried chicory root, kelp, carrots, peas, apples, tomatoes, blueberries, spinach, dried skim milk, cranberry powder, rosemary extract, parsley flake, yucca schidigera extract, L-carnitine, Enterococcus faecieum, Lactobacillus casei, Lactobacillus acidophilus, Saccharomyces cerevesiae fermentation solubles, dried Aspergillus oryzae fermentation extract, vitamin E supplement, iron proteinate, zinc proteinate, copper proteinate, ferrous sulfate, zinc sulfate, copper sulfate, potassium iodide, thiamine mononitrate, manganese proteinate, manganous oxide, ascorbic acid, vitamin A supplement, biotin, calcium pantothenate, manganese sulfate, sodium selenite, pyridoxine hydrochloride (vitamin B6), vitamin B12 supplement, riboflavin, vitamin D supplement, folic acid.
The rest isn't important really, but see that first line? That's the kind of thing you want to see. Here's a quick thing about reading labels for your pet's food:
http://www.bluebuff.com/health/readalabel.shtmlRe: the chewing. Dogs can get itchies on their skin and that can often be remedied with a better food. My friend's bichon, for example, is allergic to beef. He gets hot spots on his skin and licks/bites them until they're open sores when he eats beef. So the food he eats is a venison and duck formula with no beef. Finding that out was mostly trial and error for them from what I remember. Dogs also just lick/chew themselves, like Bildi said. As long as your dog isn't giving himself open sores or bald spots, it's probably fine.

Re: the weedkiller. Like Bildi said, I'd rinse his feet after he's been out. Also, make sure you supervise him and don't let him eat anything outside.