The best place is behind the ear, there's a fleshy pad. Get the ivermectin to room temp as it is quite viscose and harder to inject when cold. You have to be confident, quick and precise. Lots of videos if you do a google search, how to inject a pig! I used to slap my pig whilst she was eating, to numb it, then jab. Helps if you slap each time they eat, they then get used to it, a few days later slap then jab, hopefully they won't notice, sounds odd but it worked for me until I bought a masterject vaccinator.