The product I am using currently is Aspen Ivomax, but I have used a few different brands of the injectable. This is the 1% solution. I put it on some of their wet food, and they will still eat it even though they seem to taste it. From my experience taking it myself it is bitter. I make sure to put enough food out with it that they don't get as strong a taste, but still finish the food in one sitting.

Ivermectin Sheep Drench is what I use. Its about $35 for an 8 oz bottle and if you have a small dog, the bottle will expire before you use it all. Thats how little you need. A drop on a biscuit for my 98 lb doberman, an example. Its available at any feed store like Tractor Supply, and I've even ordered it from Amazon. The recommended dose is 0.034 cc per 10 pounds of body weight, or approximately 0.1 cc per 30 pounds of body weight. So you see you need the right small syringe. I dont mix into food unless they are very hungry. I hide in a treat or squirt right into their mouth.