As Janie suggeste a large box trap is the best answer...
Now here's the tricky part... What to do with Mr. G-hog once you have him trapped??? Hefre in Virginia it is against the law to take him off and release him... But that what I do anyway with racoons and groundhogs... I just make sure that I put trap and all in the back of my Toyota station wagon so that the cops don't see me transporting said animal in the back of the pickup truck which has no tailgate....
Shy of that, the .22 is next best and fast...
But a groundhog in yer veggie garden even for one night means an entire 30 foot row of beet demolished... These animals will go thru yer veggie garden like Grant thru Richmond...
Si I trap them... My trap is about 4 feet long with a 18"X18" opening... That's the size you need...
Animal shelters will sometimes lend them out to you...
Apples, peaches and just about anything that has a sweet odor will work as bait...