@CarrieGSD Is your GSD anxious around all new people (and perhaps in new situations) or just with visitors to the home who she doesn’t know? Is she a young dog? Does she simply bark at visitors to the house because she’s overstimulated, or do her hackles go up and does she lunge towards them in a threatening manner? How do you currently deal with this?
It’s surely worth taking her to training classes, where she’ll have to encounter strangers and other dogs (but in a controlled environment) to help with her socialisation, or seek the advice of a behaviourist
The suggestions to trial a short sit with a paid sitting service is a good one IMHO. If you do decide you want to leave her with THS sitters in your own home, please do be transparent about her trust issues in your listing and, during the video chat, let the sitter(s) know all about her, including her triggers (and how you successfully deal with them), her routine, what commands she knows, where she sleeps, what her favourite toys are, if she has treats, what she’s like on the lead, what her recall is like, what she’s like around other dogs and people, games she likes to play, if she’s allowed on furniture, whether she’s not allowed in certain parts of the house, how long she can be left etc.
it would seem imperative to invite sitters to arrive the day before your departure, so your girl can do a calm meet and greet and observe the sitters in your home with you before she’s left alone with them. Sitters who’ve experience with dogs will ignore her, letting her come around in her own good time, and will always make their presence known before entering a room, to avoid surprising her into barky-mode. One idea - and this might sound a bit weird - is to ask your sitters to bring some old, worn clothes, and leave a few items around where your girl feels safe, so she can get used to their scents when they’re not actually in proximity to her. Or, give them something they can wear next to their skin for a while - even if it’s tea towels - and then leave those near to your dog’s bed and food bowls etc.
We’ve done sits for rescues with trust issues and one sit included 3 dogs who had previously experienced abuse and horrible neglect. We agreed to do a test-sit of a few days, (the HOs went to stay with family) before agreeing the longer holiday sit, so this might be something to consider (with full disclosure), perhaps after your paid sit. In this case, all went well - from all perspectives - and it was genuinely one of our happiest and most positive sits and we had no problems whatsoever with any of the dogs (who actually had gorgeous characters and very quickly bonded with us once they realised we did fun things with them and used positive reinforcement methods, rather than being a threat).
I’d suggest considering sitters who sit as a couple and who have experience with larger breeds of dog, confirmed by a substantial number of reviews and photos. As sitters, we have many hundreds of photos of our sit pets, so any applicant should be able to supply pics of them with other guarding breeds.
You know your dog better than anyone, so it’s your responsibility to properly assess the risks:
You’ve already found your girl is fine when boarding, so maybe this guarding is a territorial thing and it’s your presence and her home which sets her off. I must just say this: if in doubt (regarding safety issues), don’t.