The former Ireland captain admits he has difficulty producing a settled side to take on the All Blacks in the three-match series this summer.
"Selection is incredibly difficult. I have written my team down but it changes from week to week. I have written down five different teams for five different styles of play," he said.
"One team for experience over youth, one team for loose rugby, one team to dominate up front and so on. In the end it is all an exercise in futility."
Wood - a prominent figure on the last two Lions tours to Australia and South Africa - warns the toughest of all touring destinations awaits whoever makes Woodward's squad.
"Players selected for the Lions will give every bit they have for the chance of being victorious in New Zealand, which has proved to be the hardest place to go. The Lions have only won once there," he said.
"The Tests will be hard, aggressive and brutal. The midweek matches will be attritional, much more so than in Australia.
"It's going to be very, very intense and difficult and well nigh impossible for the players to get away from rugby."