Continuity mistake: The Bringloidi leader keeps saying that they've spent 300 years building their society, but this episode takes place in 2365, and it's stated that his ship launched in 2123, making it 200 years.
Continuity mistake: In the beginning of the episode, Riker, Geordi, Worf, Data, and Pulaski are playing poker. Pulaski puts two neat stacks of chips in the center beside some chips in a pile. It then shows Worf putting similar stacks in the center but Pulaski's stacks are not visible and they should be. Then when Worf wins the hand, the camera is showing a wide shot of him pulling the chips towards him and you can see his and Pulaski's neat stacks of chips.
Continuity mistake: When Data is dealing the cards for 7-card stud, they show him dealing 1 card to everyone. In the close up, he's now dealing everyone a 2nd card. When it cuts to his hands however, everyone only has 1 card and he's dealing them a 2nd card again.
Visible crew/equipment: As La Forge and Crusher leave the bridge, and the camera closes in on Riker, there's a shadow of a piece of filming equipment on the wall behind and to the left of his head, at the upper right of the shot.
Visible crew/equipment: As Picard goes to sit in his seat, there's a shadow of the boom mike playing across the wall above Burke and Kolrami's heads.
Revealing mistake: When looking at Kolrami, the line between his make up and actual skin tone can be seen between his scalp, hairline, and the back of his neck.
Visible crew/equipment: As Kolrami talks to Picard from beside the aquarium, you can see the studio light panels reflected on the glass.
Continuity mistake: Near the end, when Pulaski finally stops the infection in Riker and is just about to contact Picard with her success, look at Riker lying on the table. His eyes are open, then he closes them slowly. The next scene has Riker opening his eyes for the first time after recovering from the procedure.
Other mistake: In this episode, in Riker's memory, the encounter between him and Quinn is re-lived. As Quinn starts to attack Riker, you can see Riker's stunt double's face, and tell that it's Quinn's stunt double, as the hair is smooth, not styled. Also, Riker is a few inches taller than Quinn, but in the onset of the attack, they're equal heights.
Continuity mistake: After Pulaski examines Riker's leg, and readies to beam up, he leans to the right to get up. In the wide shot, he does it again.
Continuity mistake: In the opening sequence, the ship is positioned so that Shuttle Bay Two is aimed at the phenomena. But a moment later, the ship is facing into the stellar material.
Who Watches The Watchers - S3-E4
Visible crew/equipment: Just after Nuria says "your power is truly boundless" a few seconds later a microphone can be seen dropping and quickly being raised again at the top of the window.
Who Watches The Watchers - S3-E4
Revealing mistake: About 38 minutes into the show, when Dr. Mary Warren dies and there's a close up of Picard & Nuria, you can see the her hand moving up and down as she breathes.
Continuity mistake: When Geordi falls down the hole in the beginning of the episode his visor is seen to his right. When he wakes up he finds it to his left.
Continuity mistake: After Wesley makes his neutrino pulse suggestion, Picard tells him to go do it. Wesley walks off camera. Then there's a commercial break, and Wesley is back on the bridge in the long shots. A few minutes later we hear the turbo-lift and Wesley walks back onto the bridge.
Visible crew/equipment: When Riker first beams down he uses a flashlight - if you look closely you can see the electrical cord that runs down his sleeve to an off-screen generator.
Other mistake: During his final discussion with Tomalok, Picard tells him that the Enterprise will escort the Romulan ship back to The Neutral Zone. However, as the episode ends, the two ships are heading off in opposite directions. Both the Enterprise and Romulan warbirds have demonstrated in the past that they can spin on their axis from a standstill. There is no reason for either ship to head away from the other to turn around.
Other mistake: While down in the pit Geordi makes a couple of spikes to climb out with. When the phaser beam is melting the ore, the metal goes molten about two inches in front of the beam. Also, the spikes are rounded, like handles. The molds he made would have left a flat side.
Other mistake: As Troi describes her idea of "real" chocolate to the computer, it interrupts her with a warning about the nutritional value of her request. The reply is in two parts, and between the parts, you hear the intake of breath, something no computer would do.
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.