I have a 6 year old malinois (possibly a mix, she didn't come with paperwork)
When we got her, she was crate trained, never gave us any issues going into the crate, happily went into it and let us close the door and leave. My wife and I work different schedules, so normally she was only in there for maybe about 4 hours, if it was much longer than that we always made arrangements for her to stay with my parents or at least to have someone stop by to walk her.
However, she's too smart for her own good, and at some point she figured out that she could escape the crate, and there was no putting that cat back in the bag. No matter how we tried to secure the crate she figured out a way to squeeze out. We got worried that she'd hurt herself trying to get out so we started leaving her loose.
And at first everything was fine, she maybe got into the trash a couple times but overall we had a few good years of her being loose by herself in the house without any major issues. After a few months of having free reign of the house she never really went into the crate anymore and found other "den" areas around the house, so we packed up the crate.
Lately though, she's been getting bolder, stealing things off the counter (she pulled the whole bread box down the other day,) she got into a bottle of vitamins (that was a fun vet bill) etc.
She's not being destructive otherwise, not chewing up the furniture or anything, she doesn't even always eat or try to open any food and such that she steals (I came home to a fully sealed bag of tortillas on the bed the other day, she absolutely could have torn that open if she really wanted to)
And she does get a lot of walks and playtime, nothing has really changed in our routine that I can think of that would account for this change. It feels a lot like she just let the intrusive thoughts win one day to steal something from the counter and it's just snowballed from there.
Right now we're doing what we can to secure anything that seems like it might be tempting to her or that we're especially worried about her getting into before we leave, and we're providing her with some longer-lasting puzzle toys and treats to distract her when we leave.
So far that seems to be working, I feel like as long as we can keep her busy for the first 20 minutes or so after we leave, we're probably ok.
But we're also considering the possibility that we may need to start crating her again in a more escape-proof crate.
So in case it comes to that I'm looking for advice from anyone who's had to do something similar.
She has so many toys, big ones, small ones, toys that squeak, toys that crinkle, plush toys, harder toys to chew on, balls of all shapes and sizes, she's spoiled in that regard.
I've found that toys by themselves rarely suffice for enrichment. They want to interact with living things. If you throw legal garbage (like the core of a toilet paper) around for her to fetch for 15 minutes, it will bee worth more than a day of access to a mountain of toys without anyone to pay with.
This will sound weird, but another dog might just be what she needs.