Deer and rabbits can do a lot of damage to hosta plants by eating the leaves. You can physically deter the animals by erecting fences. But deer can jump over many fences, and rabbits can burrow under fences.
I've found that spraying the hosta plants with liquid repellents is very effective to reduce or eliminate animal damage. Follow the package directions for products such as Tomcat brand Deer and Rabbit Repellent, or Liquid Fence brand repellent.
The trick to effectiveness is to begin spraying your plants very early, when the pips are just beginning to emerge from the ground and the leaves are unfurling, and then repeat every 3-4 weeks depending on the amount of rain, which can wash off the repellent. So keep an eye on the weather report when it's time to spray, and don't waste your money spraying just prior to a big storm.
Deer and rabbits are smart and remember their food sources, and also remember where there is not food. So start spraying early to train them that your garden is NOT a food source, and they will leave your garden alone later in the season, even if you extend some spray intervals.