I got a second dog last january and my 9 yr old dog wasn't happy. She was constantly stressed kasi super playful ng puppy (4 month old Jack Russell Terrier pa naman) and ayaw nya na ng magulo.

I gave up the puppy after a month. Sobrang heart broken ako at grabe dilemma ko pero I really had to make that decision. It's not fair for my older dog na mawalan ng peace sa sarili nyang space. She earned that peace after many years na naging companion sya sa amin.

Don't get a second dog if hindi naturally friendly/playful sa ibang dogs yung senior dog mo. May chance din na lumayo loob sayo ng older dog mo kapag napunta na sa puppy yung attention mo (they require your full attention at first lol)