Nesting ducks

Hello,

Yesterday morning I noticed a pair of ducks wandering around my garden intermittently checking out the undergrowth & bushes. By the afternoon they had disappeared so I assumed they’d moved on; however this morning the female is wandering around on our lawn again. I’m really concerned that they have nested somewhere because we have a dog, I’m worried about letting her out in the garden in case she scares them away. Any advice please? Thank you