trimming

I am using autocad 2004 and I'm drawing a floor plan. I xref in the 2d points including levels and string lines etc (created using a theodolite on
site by a surveyor) and bring them in on layer 0 and lock the layer, but when trimming or extending I am able to select the seperate lines on the xref which I do not want to do so I then locked all the layers in the xref but I can still select them when trimming and extending as the cutting line. The last version of Autocad I used was r14 and have only just recently changed, is there a way in 2004 to stop the selection of xref lines or is it something I am going to have to get used to? I think once a layer is locked you shouldn't be able to do ANYTHING with that layer, it makes no sense to me.
anyway, any usefull replies will be appreciated
Mark
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Mark wrote:

Locking has nothing to do with what you're experiencing. Using a line to trim/extend doesn't modify the line, therefore locking is a non-issue.
I don't think there is a way to get the behavior you want, anymore. I've been wishing for a 'no-snap/select' layer setting for years.
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