16 month old and older dog

Before I get to my question, re-homing or crating the dog during the day is not an option. He hasn’t snapped or growled so we aren’t going to punish him.

I have a 16 month old who loves to grab my older dog (14 year old dachshund). What are some things parents have done to stop this? He thinks it’s funny to make the dog yelp. I put an end to it as soon as it starts every time but he tries to go back to it. I just want to know if anyone else has gone through this and how they worked through it. I get down on my sons level and explain to him that it hurts the dog. I am hesitant to spank in this instance because I’m trying to explain it hurts the dog so how can I use something that could hurt the kid as a learning tool.... thoughts. Be nice, He’s my first kiddo, I’m learning and not perfect.