Since it is your dad's birthday, you should buy a practical and solid birthday gift, because parents will not approve of their children spending money recklessly. However, you said you are not short of money, so I suggest you give your dad a digital camera, which is not only practical but also high-end. If your dad is interested in photography, it will be perfect.
There are other practical items that can also be used, such as razors, belts, ties, lighters, wallets, which your dad can use, and they are given by his children, so he will definitely like them. You should also choose one.
Finally, you should also pay attention that if you can't be with your parents often, buy them a small pet, so that your parents will not feel bored; or directly send your parents to travel, so that they can see more beautiful mountains and rivers, so that they will be in a good mood and exercise their bodies. Isn't this the best and most thoughtful birthday gift!