The two sides could not be separated in a 0-0 draw, with Deeney paying tribute to Cardiff for the way they earned their share of the spoils.
"I just tried to put myself about and I had a good battle with the Cardiff centre-backs," Deeney told Sky Sports News.
"I was already off running when Marshall pulled off that save, but that is why they are top, they grind out the results.
"We have to learn to do that ourselves. We are waiting for Hull City to slip up and we must capitalise when they do."
Watford, in third, are three points behind second-placed Hull in the Championship.