My dog's first Christmas in the house, I got a smaller tree and put it on a box... higher than his head. Since he couldn't sniff the base, he didn't think to pee on it. I let him smell and investigate the top in my arms.
The next year, we put it in a playpen... again, he couldn't sniff the base and we let him investigate the top in our arms, and he didn't go on it.
The third year, we just got the tree, and let him sniff and investigate while we were watching... he sniffed, said, "Oh, that inside tree again," and ignored it. He's never gone on one since then, and it's been 7 years.
