Continuity mistake: When Picard, Ro and the others arrive at the refugee camp to meet with Keeve Falor, the type of uniform top Ro is wearing has its zipper at the back in the center - with no seam whatsoever at the front. When she kneels down in front of the young child, it has changed to the open-front jacket type, so Ro can touchingly give it to this child.
Continuity mistake: When Ro and Picard are among Ro's people and she gives her jacket to a child (saying something like 'this is what I was, once') she never removes her commbadge. However, there's a commbadge neatly placed on her grey tank top - even though she didn't even remove it from the jacket, let alone put it on her shirt.
Continuity mistake: When Dr Marr and Data are talking in the cave about her dead son, she is holding the tricorder upside down.
Continuity mistake: When the Enterprise activates the deflector dish, there are four points emitting beams. However, there are five beams emitting after the angle changes.
Continuity mistake: In the scene where Data is brushing Timothy's hair into a copy of his own hairstyle, he stops, kneels down and asks Timothy "Timothy, are you having bad dreams?" In this shot there is a big tuft of hair on the right side of Timothy's head that sticks straight out. When their conversation is over and Data stands up in the wider shot, all of Timothy's hair is in place.
Continuity mistake: In Ten Forward, when Deanna and Data are done playing 'chess', the positions of The Game-pieces on the lower board level between them changes repeatedly, depending on camera angle.
Power Play - S5-E15
Continuity mistake: On the planet's surface, when the away team are knocked unconscious their positions on the ground differ significantly between shots.
Continuity mistake: In the very first scene, where Data is shuffling the cards, you can see his silver and gold chips are neatly stacked up straight. The camera then cuts to Commander Riker and then back to Data and his chips are crooked at the top and at the bottom.
Continuity mistake: When Picard looks down the mountain to look at the town he has a straw hat in his left hand, next shot it's gone.
Answer: Yes. The doors to the holodecks can be locked when in use by anyone aboard the Enterprise so they couldn't be disturbed. However, high ranking officers like Captain Picard could override the doors as it's seen that overrides are in use even for the crews quarters. Even Barclay, when he's indulging in one of his fantasies could have the doors to the holodeck unlocked by an override code.