Rhododendrons: Help!! It's dying!

I have two rhododendron's from this past summer. I wanted plants for a covered porch that faces the north. These were amazing plants...until winter. I was instructed by where I purchased the plants to bring the plants indoors until I was ready to replant them outside because in the pots the roots would be fragile.

That was in October. Now, BOTH the plants are dying...leaf by leaf. They just fall off. Some will look burnt and stay on and some will look burnt and fall off. Some will look healthy and fall off. I even repotted them with fresh soil a few weeks ago and they still are dying very quickly.

I don't see any insects or diseases. My only suspicion would be that I have a very old indoor dog (male) that is having bladder problems. I have seen a few times that he has urinated on the ceramic pots. They are huge pots / plants so the urine cannot get up into the soil but could it be that the urine is being absorbed into the ceramic pot and killing the plants? I just don't know and I hate to loose these amazing plants. They were so vibrant / healthy and beautiful. Now, they aren't.

 

When you brought these indoors, did you place them in an area that's room temperature?

 

Yes, I placed them in the dining room / foyer - which is very open and gets very good light. I do like my house kept at about 68 degrees and keep the vents closed in most areas of the house so I tried to place them where the air would not blow directly on them when the heater kicked in. But, I know it still gets dry during the heating season.