Namenda and Aricept do not fix anything. The synapses that are broken stay broken. Those that are going to break will break. What is does is rev up the other synapses so they work a little better and can compensate for the deficiencies. Pretty much what antioxidants do. The improvements show were determined by improvements in ADLs (Activities of Daily Living). Can they brush their teeth, fix a glass of milk, or put on their pants. Short term memory improvement is not in that list nor are other cognitive functions.
All any of these will do is a slight slowing of the disease in some people. None of it is a miracle cure that will give Mom or Dad back their cognition.
As for the good days and bad days... that is the way the disease progresses. It is not a constant decline but an up and down with the ups not as good and less frequent and the downs a little worse and more frequent as time goes on. Mom had some really bad days three years before she was diagnosed. In hind sight I know what they were but at the time it was just a mystery. Yet after her diagnosis she had some really good days that made me wonder. Just know this is a normal part of the disease.
As for the gun... if he makes it impossible to distract or delay him then do what I did. Let him have it minus the firing pin. Taking out the firing pin renders it useless. Then when he complains it doesn't work take it back to have it fixed and repeat the process
Dad never did figure out that his pistol didn't work.!