The trick to pulling off a good prank is catching someone off guard. Do something different in areas in which your husband trusts you. For example, if you put hot sauce in an omelet as a prank for your husband when you never make omelets or he doesn't like omelets he'll probably be suspicious. Do something unusual to something that is usual. Here are some ideas.
1. Fill the salt shaker with flour or sugar. Unless you've pulled this prank before, he probably won't examine the salt shaker before pouring it over his food.
2. Switch your drawers. Put all your clothes in his drawer and all his clothes in your drawer. You may have to do this before he wakes up in the morning or while he's out so you don't get caught.
3. Type up a letter from a close relative or friend saying that they just won millions of dollars and want to give your husband a few hundred thousand. It would be even better to have the relative hand write the letter and call to talk about it over the phone. If he falls for it, make it last as long as you can, but you better tell him the truth if he's about to max out all his credit cards. No prank is worth years of debt.
4. Have a friend you know that he doesn't or has never met happen to run into him at a restaurant or store claiming to be an old friend from high school or college. The person should claim to have dated him or at least done a lot of things for him. Otherwise your husband won't feel very guilty about not remembering.
5. Fill the lemonade container with lemon juice instead of lemonade.
6. Put ketchup and mustard on his seat at the table. If he's the kind of person who would notice that instead of just sitting down, whoopie cushions and pins are still a great idea. Even better, put glue on a chair. Start making out with him and get him to take his pants off before getting him to sit in the chair.
7. Call him at work. Tell him you're at the police station and that you've been arrested. If he falls for it he'll probably go to the police station to get you. If he calls you don't answer the first few times. See how long it takes for him to figure out you're really just waiting for him at home.
8. If he's working on April Fool's Day have a friend or one of his co-workers send him secret admirer notes throughout the day. Maybe even chocolates and flowers. Make it appear that the person is obsessed. It may even be a good day to start a few days before April Fool's Day.