I will stick my neck out and say that I think it is impossible to detect intelligent design in the universe for the simple reason that the whole detection concept is based on false premises.
The point is not that you cannot detect design, but that the very idea of detecting design as assumed by ID proponents, whether they be covert religious fanatics or non axe grinding secular investigators, is fundamentally flawed.
ID detection falls flat on its face, because it represents a classic example of the begging the question fallacy, where you assume the existence of the very thing you are trying to prove.
As an example, let's say I proclaim the existence of unicorns by pointing at evidence in the form of strange hoof-like prints in some soft mud on a riverbank. As I am already convinced that unicorns exist and have a good mental idea of what they should look like (although I have never actually seen one) it is very easy for me to mentally fit any evidence I come across into a unicorn shaped schema.
Now, of course it is possible to identify animals such as badgers and rats from just the marks they leave in mud. In fact whole books have been written on this subject alone. However, the difference between a unicorn and a badger is that we know the latter exist and therefore have to assume nothing.
In the case of the unicorn, I am (in this example) bringing into existence an extremely complex 300 or 400 lb animal, complete with internal organs, bones and eyes etc, all on the basis of a few marks in some mud.
If you think that is an impressive conjuring trick, then look what ID proponents are doing. Taking this or that incomplete or poorly understood scientific phenomena, they conjecture into existence a being so omnipotent that it can create whole universes.
There seems to be more than just a slight mismatch between the evidence going in and the conclusions (which appear to have been conjured out of thin air) coming out.