How does the body make sure that Vasoactive Intestinal Protein reaches only the target tissue?
Vasoactive intestinal peptide (VIP) acts in the intestine, brain, kidneys, lungs, heart, blood vessels, etc. (Cardiovasc Res) and its effects all lead to the same goal: to improve the delivery of blood, glucose and oxygen to the tissues, so it's not a problem if it acts on different tissues simultaneously. Specifically, VIP stimulates thirst, water retention and blood flow through the coronary and pulmonary arteries, dilates bronchi and breaks down glycogen to glucose, among other. 

VIP can act via the nerves as a neurotransmitter or via the blood as a hormone:


  In research animals and in humans, VIP, administered into the coronary
  artery or intravenously, increases the epicardial coronary artery
  cross-sectional area, decreases coronary vascular resistance, and
  significantly increases coronary artery blood flow. High frequency
  parasympathetic (vagal) nerve stimulation also releases endogenous VIP
  in the coronary vessels and heart and significantly increases coronary
  artery blood flow. (Cardiovasc Res)


In humans, VIP stimulates water retention and thirst:

1) VIP stimulates the secretion of renin:


  VIP has now been shown to produce an increase in renin release in a
  number of species, including humans. (Ann N Y Acad Sci)


The activation of renin-angiotensin-aldosteron system results in water retention.

2) VIP stimulates the secretion of vasopressin (Cardiovascular
Research). Vasopressin stimulates water retention. Since vasopressin (arginin-vasopressin or AVP) is dipsogenic (stimulating thirst):


  given the established dipsogenic effect of AVP in the nonpregnant
  state... (JCI Insight)


and since VIP stimulates the secretion of vasopressin, VIP is also dipsogenic.

Now, there seems to be some conflict in the studies about VIP being dipsogenic or anti-dipsogenic in rats:


  VIP was found to have no effect on drinking when injected centrally
  and peripherally in the eel, although it is dipsogenic in the rat
  after central injection. (ResearchGate)
  
  Intracerebroventricular administration of vasoactive intestinal
  peptide strongly inhibited drinking in rats deprived of water...
  (Neuropharmacology)


Not to go in the details, but there may be different circumstances, for example, the level of dehydration, in which VIP can act differently...