I find that making homework meaningful is becoming increasingly challenging. Let us suppose that I am planning for next semester's first-semester or second-semester calculus course at my university.
In all likelihood, we will be using one of the common calculus texts because the university expects consistency, both from semester to semester and from teacher to teacher. Solutions manuals exist for most of the common calculus texts, so assigning problems from the text has downsides. But this point is slightly moot, because WolframAlpha can do essentially all the problems anyway (albeit with poor exposition). There is also an endless supply of answers awaiting at Math.SE and similar fora.
Unfortunately, writing my own exercises (which I currently do) doesn't prevent or penalize the use of WolframAlpha or online math fora.
One possible solution would be to make homework count much less. But I dislike this idea, as I find that students who do homework are much more competent on average than those who don't; homework should be consequential enough for students to take it seriously.
What are possible, good ways of overcoming the availability of free and proficient homework assistance?