I would highly recommend the 2 Frick OLEAs (off-leash exercise areas) that menge101 linked to.
Many many people do not follow the leash rules in Frick park which ruins it for those of us that have older dogs that don’t want young dogs running up on them; and as a result are seen as “not friendly”.
They are both fully fenced with 5-6ft chain link and have air-lock style entries to reduce the risk of off-leash dogs running out when someone enters/exits.
They both have benches for patrons to sit on/at and a few things for the dogs to play in/on/around. Obviously you will have a mixed bag of people and dog types using the OLEA, so your mileage may vary but you run the chance of seeing annoying/aggressive dogs and inattentive and/or jerkish owners at any dog park.
I would only recommend Hot Dog Dam if the dogs you are sitting for have a good recall as that OLEA is not fully fenced in (I haven’t been there in a few years, so hopefully this has been fixed). The dog area is/was separated from the jogging trail by a split-rail fence and chain link, but the hill on the far side of the eponymous Hot Dog Dam is not fenced off at all and leads right up to a highly traveled road and intersection (Forbes and Braddock Avenues).
That being said, this OLEA is awesome for dogs that love playing/jumping into water or need a bit of a cool down or non-soapy rinse off from other activities.
I fish pretty regularly up at Lake Arthur. Its around 45-55 minutes from Pittsburgh. You can rent a boat there if you want to get to some better spots.
Typically fish North Shore area, and I catch Largemouth Bass / Catfish / Panfish. I pretty much target bass, and use plastics / spinner baits. In the late evening you catch Stripers up there.
Although its fished pretty heavy, there are places on the shore to fish around the park. Go up early morning / late evening.
Also Lock 3 in Cheswick is worth checking out in my opinnion. Park near the warehouse across from Lock 3 bait and tackle:
811 Freeport Rd
Cheswick, PA 15024-1209
Go early morning or evening, get some minnows and fish the waters below dam. You’ll catch bass, walleye, gar and sometimes musky.
Who knows what else is lurking in there!
We visited Rickett’s Glen a couple years ago and loved it. The Ganoga Falls trails were brilliant, and there was a beautiful beach hidden there as well.
Ohiopyle has some beautiful falls. The river’s great to look at, even if you aren’t doing any rafting or kayaking and Ohiopyle itself is a fun little town.
Make time for Cucumber Falls and the Natural Waterslides.
Besides Ohiopyle, have you gone to the Delaware Water Gap (Bushkill Falls are in the same area)? The Lehigh Gorge? There’s also Hickory Run State Park. Traversing a boulder field is always a lot of fun.
In the area, I’d especially recommend either the Bear Run Nature Reserve. There are several hundred acres of wood and trails that surrounds Frank Lloyd Wright’s Falling Water house and the Fern Cliff Natural Area.
The latter is pretty small, but has many great views of the river.
Laurel Ridge State Park is also a good series of trails. The benefit to it is that pretty much every west-east road through the southern half of the state passes through it and have trail access. Good trails, many nice views.
Conemaugh Lake is one that doesn’t get a lot of press, but is really cool. An combination of trails and an old rail right of way cross a series of oxbow bends in the Conemaugh River Lake. The views are incredible.
Similar can be found up around Kinzua Lake near the NY border.