Penny Proofing the yard

(Penny the beagle and Jack the black lab)
I didn't mention it, but Saturday in her first five minutes at home Penny took off. She went to a low spot in the picket fence and was under and gone in a second, me in pursuit. She ran down to the river and dove in after the 5 ducks that had been sitting there. She seemed to be surprised to be swimming, and came back to me. I bought steel mesh and spent Sunday digging around the fence bottom and stapling this stuff in place. I will keep an eye on her: typical beagle, sweet lap puppy in the house, chasing ducks and squirrels outdoors.
Our dog Petey was a beagle or some kind of hound mix, and I grew up with hounds, so yes, I know how they are.
I am guessing this is how she became a stray and ended up at the shelter.