Dr. Pam wrote this on another post :

Do NOT give your dog Ibuprofen unless you want a stomach ulcer.  It is not a good choice for dogs anyway, and combined with another NSAID like Rimadyl it doubles the risk for problems.  Also do not use aspirin with NSAIDS and do not use Tylenol either.

 I have heard terrible stories about Rimadyl

Comet did Rimadyl for 1 1/2 years daily. She was always 3 legged and she had both of her back knees go out and had TPLO surgery in them.  So, her body really needed something when she was around 11.  I, too worried but her ortho vet reminded me, it's better to have them feel good than to worry about something that may never happen.  And even if it takes time off of their life, it's better to have them feeling good.

She actually died of cancer (hemangiosarcoma) in the end which was diagnosed the night she died.  (she was bleeding out)  In looking back, I'm so thankful for her being on Rimadyl because she actually did have cancer in her body – at least for 2 months.

If I do-overs, I would have rather been on metacam, like Samson.  Although, I guess it doesn't matter since she had no side effects. 

But just so you know, aspirin can cause problems short term.  My friends put their dog on asprin because their dog blew a ACL ligament in the knee.  So, they only did aspirin (not knowing it was bad) for a couple of months. They did the surgery and but the vet didnt know that her stomach was completely ulcerated.  She never recovered.  The autopsy revealed what happened.

Maybe you can get a switch to Metacam from your vet.  If he tolerates it, then you can get your vet to write a RX and you can fill it at Walmart for cheap.