Lessons learned six years into owning my first dog:
1. Training is everything. And it's not just the sit, stay, down stuff either. It's about letting your dog know exactly what is expected of him in each and every situation. My dog, for example, has been trained to ignore other dogs while he is on leash so that walking him isn't a nightmare. We used Dog a Training for Dummies and took a series of four classes from PetSmart (puppy, intermediate, advanced) that were surprisingly good. I think they were $120 for each 6-week class, so a total of 18 weeks of training. Well worth it, and the group setting is great for getting your dog to listen to you when there are distractions. We also did agility for about a year, but stopped when it got too competitive. It would have been pretty expensive to train to competition levels.
2. Vet bills. If you get a puppy from a breeder that needs to be spayed/neutered and have its shot series, it's going to be VERY spendy. Turns out my purebred had lots of unidentifiable health issues. Tremors, skin irritations, etc etc. We've probably spent $10k on vets, including several specialists and in the end he's just sort of broken and we deal with it. Google, Google, Google if it's not a broken bone or a seizure or something. We treat his skin with a product we found online that the dermatologist had never heard of. Monitor a condition for a while so that you have good info to go to the vet win because half of diagnosis is behavior and frequency.
3. Food. I'd recommend just going with something grain free from the start. My dog has grain and chicken allergies, and he eats Natural Balance Limited Ingredient Diet. Currently he's on Kangaroo and Potato because he hates sweet potato and the rabbit gives him gas. Seriously, he's a mess.
4. Toys. It seems like all dogs are either fetchers or tuggers. Buy one of each kind (NOT the rope kinds, as the dogs can tear them apart, ingest the strings, and get a blockage) and see what your dog likes best. My dog has about 30 toys and probably needs 3. Squeaky tennis balls for outside, this weird hollow hex ball for inside, and his chuck it frisbee for swimming.
5. Crate train! My dog went from a crate to an exercise pen to free reign of the house by the time he was about a year old. He just got more privileges as he became more reliable. Still loves his crate for travel or if he's feeling mopey.
Hope that's helpful! We got out dog well before we knew anything at all about money, let alone Mustachianism, but I don't regret having him at all, though I'd probably have approached his early years differently. Despite his issues, he is the most amazing companion you could ask for. We just get each other. I hope your experience is as positive!
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We also have a dog with food allergies so he eats Natural Balance limited ingredient rabbit & sweet potato food. We feed him carrots & green beans for snacks in addition to some limited ingredient treats.
We buy toys with no stuffing and spend a little more (nothing from Walmart) Don't buy any treats or snacks made in China. Be careful of rawhide chews/sticks. Really watch your new dog or puppy around his toys, you can spend a fortune having surgery if they ingest and not pass a piece of plastic.
Really read up on people food that is poisonous to dogs (chocolate, grapes, chewing gum, onions, etc.) Also what household cleaners & yard fertilizers/chemicals you use. Know what plants are in your yard and if they're toxic to dogs. In addition to your house, puppy proof your garage.
We crate trained our dog and he automatically goes in his crate when we are getting ready to leave the house for a few hours. It gives us piece of mind to know he won't get into anything while we're gone.
When socializing your new puppy be a little wary of other dogs off leash at dog parks, their owners may say they're friendly but I've had my dog snapped at more than once by what was " a friendly dog". Also you don't know if they have kept up on kennel cough, etc. and your dog could have all his shots but a chance encounter at the park could cost you an unexpected vet bill. I had my dog off leash at a dog park and strangers there will want to feed him their treats, bring along some that you know are safe or just be firm in not letting them feed your dog because they could be cheap snacks that will get your dog seriously sick.
Vet bills: In addition to the checkups and shots be prepared to shell out hundreds of dollars a year with random trips to the vet. We've had three dogs with no health issues before our latest dog and he really is a special needs dog. We paid more money for him but we now think he was from a puppy mill and we've also paid more in vet bills. So when you get your animals, hope for the best but be prepared for the worst, emotionally and financially.
Even though we've had so many health issues with our dog, he's worth every penny we've put into him. He takes us for a walk every day & encourages us to be healthy and enjoy the outdoors. When you look at the world from they're prescriptive it really changes you as well.
BTW, be prepared to tell your family that your dog will be cremated and buried with you & your spouse.