Gardening with dogs can be a challenge and frankly, you'll never have a great garden if you allow the dogs to run free all day long in the backyard. What I do (I have 6 dogs) is allow them to run in the yard when I'm working in it, but I don't leave them alone out there unsupervised all day long. If I can't be with them, I keep them in the house or in some nice kennels where they are protected all day long. Also, dogs get bored left in a backyard so I highly recommend that you walk them regularly away from the house which will give them exercise and will keep your yard from becoming one big bathroom for them. As far as toxic plants are concerned, I would not worry too much. There are many common plants such as yew that, in theory are toxic if eaten, but dogs rarely will chew on plants like this because they taste bad. One other tip I've learned is that if you want to have a garden and dogs that you fence part of the garden off to protect it. Just don't expect to turn the dogs out in the morning every day and come home from work and see a perfect garden. That won't happen unless your dogs are either small breeds or elderly.