I've hunted the creatures for close to 50 years now in PA. First in western PA then for the last 30 years in eastern PA. I'll share my experiences for whatever it's worth.
In my experience, hunting on public land is very unattractive to me simply because of the characters I've encountered. Thus I haven't hunted varmints or predators on public land in a very very long time. The best option by far is private land but its takes some effort but its well worth it.
Most farmers I've encountered will allow you to hunt ground hogs IF you approach them in a
polite manner that gives them confidence that you're safe and experienced. References also help tremendously, i.e. name dropping of other farmers in the area who have given you permission to hunt. Once you establish a good reputation in the area, it becomes a lot easier to access new farms. I'm known as the "Ground Hog Man" in the area.

And whatever you do, DON'T show up with a bunch of shooting buddies - go alone.
Always thank them EVERY time you hunt their farm, even farms where you've hunted for years.
On a new contact, ask them the manner in which they prefer you to notify them when you arrive for a hunt. Some have given me unlimited and exclusive access without contacting them. Others ask me to call them to alert them that I'm in the field. Still other prefer a personal check in before entering their farm. I ask for approval to leave a note on the house door if they are not home when they require a personal contact.
Also, ask their preference where to park. Never drive or park anywhere unless they have given you specific permission for that area. Driving on the field is the surest way to end permission unless they have given you permission to do so.
I carry a copy of PA House Bill 13 that provides liability protection for land owners giving permission to hunt on their property. Only mention this if the farmer raises it as a concern.
Most farmers in my area will not allow you to hunt deer so don't ask them on your first contract. Just ask permission to hunt varmints. Most farmers are eager to get rid of ground hogs. Once you establish a relationship with a them, you can test the waters about hunting deer. I have a few that allow me to hunt deer but it took a few years to achieve permission. Some of my best friends now are farmers - some like to talk a lot so be patient and engage them. Stay clear of politics and religious issues - don't bring these issues up and if they do be a good listener.
Always remember - you are a guest - respect their rules and property and NEVER leave any trash behind. I hope it goes without saying it but I'll mention it anyway - ALWAYS use shoot safely meaning make sure you have a solid backstop for the shot and observe all safety zone laws.