One of my favorite pictures of my dogs is standing on the beach, with their reflection clear, bright, and colorful below them. This particular photo is easier to get than you might think.
The key to getting a good reflection picture is all about the angles. But first, you must find somewhere with a soaking wet beach. Going down as the tide is going out is the best idea, both for a nice wet patch of sand and for safety. You should always be facing toward the water. If possible, make sure you go with an extra person to keep an eye on the waves. At least in my area, "sneaker waves" that are much larger, faster, and stronger than the normal waves are common. If they catch you off guard, they are dangerous. This is important because a lot of people, when taking pictures, will often tune out the world around them and only pay attention to what is in the view finder.
Now that you have an idea in your head of where you want to go, you need to get up early in the morning and get to the beach by sunrise. As I said above, the reflection in the picture is all about angles; specifically, two angles are important. The angle between the sun and the beach, and the angle between you and the dog. The second angle you can alter some yourself by moving closer or farther away, or by crouching down. The first one, you need to just get to the beach early enough to use the natural angle of the sun to your advantage.
I actually waited what I consider too long before trying for a reflection picture on this particular trip. These pictures were taken close to an hour and a half after sun rise on the beach, which meant that to get the proper angles, I had to stand farther away, use my zoom lens to get close up, then crouch down to again increase the angle between me and the dog's reflection on the beach. You will have better luck shooting these when the first full sunlight hits the beach in the early morning.
Once you are down at the beach at sunrise and have a nice wet patch of ground, start looking for that reflection. You will notice places where it is clearer than others. Move around, and let your dogs just wander or play, and pay attention to the ground beneath them to see if they are playing with reflections coming right along with them.
If you see the reflections, bring up the camera and start shooting! You don't have to pose your dog for a good reflection picture. Make sure you keep both the dog and the reflection fully in the frame. This can be hard at first because unless you are consciously thinking about it, it is easy to default back to framing just the dog, and you will miss the reflections you were aiming for in the first place.
Trouble shooting: The reflection isn't very clear. Try one of two things. Back up, or get lower to the ground. Sometimes, you may need to do both, such as shooting slightly later in the morning when the sun's angle is higher. Both of these methods will increase your angle in relation to the water on the ground, creating a clearer reflection.
If you are still having trouble, take a break from taking pictures. Make sure to have fun on the beach with your dog. Walk around. Notice where the beach is wet and where your dog has a nice reflection. Try taking a few pictures there, remembering to keep both the dog and the reflection in the frame. Keep trying in different places until you and your dog are tired and ready to head home (or head for some breakfast!). If your dog will pose for you, place them in a stand-stay in a place clear of rocks or shells on the ground that gives good, clear reflections.
I almost always shoot towards the ocean for these shots. Since I am on the West coast, that means I am shooting away from the sun. Someone on the East coast will need to let me know if it works shooting toward the sun or not.