Repairing a hole in drywall caused by a dog bite can be relatively straightforward. Here's a step-by-step guide to help you fix the damaged area:

1. Gather the necessary materials: You will need a patching kit or the following supplies: drywall patch, utility knife, sandpaper, joint compound, putty knife, mesh tape (if the hole is large), and primer/paint to match the existing wall color.
   
2. Prepare the damaged area: Start by trimming any loose or damaged edges around the hole using a utility knife. Create clean, straight edges to ensure a proper patch. Remove any debris or loose drywall paper.
   
3. Insert a patch: If the hole is small (less than 1 inch in diameter), you can use a pre-made drywall patch. Center the patch over the hole and trace its outline on the wall. Cut along the traced lines using a utility knife to create a hole that matches the size of the patch.
   
4. Reinforce with mesh tape: For larger holes, you may need to reinforce the repair with self-adhesive mesh tape. Cut a piece of mesh tape slightly larger than the hole and place it over the hole, covering the entire area.
   
5. Apply joint compound: Use a putty knife to apply a thin layer of joint compound over the hole and mesh tape (if used). Extend the compound beyond the hole to blend it with the surrounding wall. Smooth it out evenly, feathering the edges to create a seamless transition.
   
6. Let it dry and sand: Allow the joint compound to dry according to the manufacturer's instructions. Once dry, lightly sand the patched area with fine-grit sandpaper to create a smooth and flush surface.
   
7. Repeat joint compound application: Apply a second and, if necessary, third layer of joint compound, allowing each layer to dry and sanding in between. This helps build up the repair and achieve a smooth finish.
   
8. Prime and paint: After the final layer of joint compound has dried and been sanded, apply a coat of primer to the patched area. Once the primer is dry, paint the repaired section to match the rest of the wall.
   

Following these steps should help you restore the damaged drywall and make it look seamless again. Keep in mind that larger or more complex holes may require a professional drywall company to fix.

Mold growth on drywall can be prevented by taking a few preventive measures, such as:

1. Keep humidity levels low: Moisture is the primary factor that promotes mold growth. So, it's crucial to keep the humidity levels in your home low. Use a dehumidifier or air conditioner to maintain a relative humidity of 30-50%.
   
2. Proper ventilation: Ensure proper ventilation in your home, especially in areas where moisture is high, such as the bathroom and kitchen. Use exhaust fans or open windows to increase air circulation and reduce moisture.
   
3. Fix leaks promptly: Any leaks in your plumbing or roof should be repaired promptly to prevent moisture from accumulating on the drywall.
   
4. Use mold-resistant drywall: Consider using mold-resistant drywall in high-moisture areas. This type of drywall has additives that prevent mold growth.
   
5. Clean regularly: Regular cleaning of your home can help prevent mold growth. Dust and vacuum your home regularly and clean any visible mold with a solution of water and detergent.
   

By taking these preventive measures, you can prevent mold growth on your drywall and keep your home healthy and safe.