The using pattern is nice and reads very well.

However, the implicit call to Dispose is doing a synchronous db call and blocking the calling thread so I'd love to see an option to dispose asynchronously, even if it means I can't use the using keyword in my calling code.

I guess SqlDistributedLock .TryAcquireAsync could return an interface like this:

IAsyncDisposable : IDisposable
{
    Task DisposeAsync();
}

What do you think?